Battery capacity-issue

[Georgia Mike]

I have 4 Trojan T105 batteries that are 3 years old. They have been always kept fully charged. I have 300 watts of solar that keeps them topped off when in storage. We don’t do any boon-docking at all but would like to start doing some in the future mainly just overnighting once in a while. The problem I’m having is I Don't seem to have as much capacity that I should have. Yesterday I went over to do some things at the Motorhome and both banks were at 13.5 float charging. I had some of the overhead lights on for an hour or so while working not much else. When I was finished I turned the inverter on to use the vacuum to clean up and after maybe 5 minutes of running the inverter shut down saying low battery. The low battery cutoff is set to 11.0 and it was reading 12.3 on the Magnum remote so I was confused why it shut down. Does the vacuum use a huge amount of power? I have the Amish 12 volt dual compressor unit that is connected directly to the house batteries and it draws 11 amps when both compressors are running. Both compressors cycle on and off so it wouldn’t draw a continuous 11 amps all the time but I’m afraid that it won’t make it through one night if can’t even run my vacuum for 5 minutes.

[waterskier_1]

To properly answer this question, you need to get a handle on all the leads being supplied by the batteries - that might surprise you.  I recommend a Shunt- type monitor, which along with showing instantaneous current, will also show the SOC (State Of Charge) of your battery bank.  The 11.0 Volts might be a bit high, since the battery voltage drops under a heavy load, but recovers after the load quits.  But begot you randomly start changing things, measure the load.  A Clamp-on DC Ammeter will worth to identify steady loads.  If both your compressors on the refer kicked in when running your vacuum, that could have triggered the inverter to shut down. 

  - Rick N 

[Georgia Mike]

I have a shunt meter on the house batteries and at the time the solar was adding to the bank. I did not have the refrigerator on being since it is at the storage lot. As I said in my first post the only thing on at the time was over head lights and the normal parasitic draws that are always on. 

[96 EVO]

May want to try draining them down to about 40-50% charge (12.0V), then charging them back up, about 3 times in a row.

They seem to lose capacity just sitting on float charge for a long time. Cycling them a few times seems to 'wake' them up!

[Georgia Mike]

1 minute ago, 96 EVO said:

May want to try draining them down to about 40-50% charge (12.0V), then charging them back up, about 3 times in a row.

They seem to lose capacity just sitting on float charge for a long time. Cycling them a few times seems to 'wake' them up

Well that makes sense because I never have really drained them down much, they are always fully charged.

[96 EVO]

A few hrs of equalize charge would probably do them good as well!

I take my sealed chassis batteries out of the loop before I equalize my house bank.

Edited December 5, 2023 by 96 EVO

[Tom Cherry]

2 hours ago, Georgia Mike said:

I have 4 Trojan T105 batteries that are 3 years old. They have been always kept fully charged. I have 300 watts of solar that keeps them topped off when in storage. We don’t do any boon-docking at all but would like to start doing some in the future mainly just overnighting once in a while. The problem I’m having is I Don't seem to have as much capacity that I should have. Yesterday I went over to do some things at the Motorhome and both banks were at 13.5 float charging. I had some of the overhead lights on for an hour or so while working not much else. When I was finished I turned the inverter on to use the vacuum to clean up and after maybe 5 minutes of running the inverter shut down saying low battery. The low battery cutoff is set to 11.0 and it was reading 12.3 on the Magnum remote so I was confused why it shut down. Does the vacuum use a huge amount of power? I have the Amish 12 volt dual compressor unit that is connected directly to the house batteries and it draws 11 amps when both compressors are running. Both compressors cycle on and off so it wouldn’t draw a continuous 11 amps all the time but I’m afraid that it won’t make it through one night if can’t even run my vacuum for 5 minutes.

Rick is correct.

BUT, to answer your question....here is what is in the files.... READ ON AFTER THE LINK

When I wrote this and it needs a little revision, it was very general.  BUT, here is how your determine how good your Trojan's are....and how much capacity you have.

• FIRST, having them load tested is a waste of time.  Lifeline AGMs and Trojan's manuals both, I think, say...  LOAD TESTERS WILL NOT WORK on Deep Cycle. I printed out the Lifeline page 22 on how to TEST.  It is the best that I have seen.  YES, that is for an AGM, but it is applicable to Flooded...so it works for your batteries.....see the file page that I is a PDF
• Basically, the Trojans need to be exercised, drained to approximately 50%, about every 6 - 9 months.  That procedure is in the Battery 101 paper.  However, here is a little more "info" that I will add.
• The best device to run them down is a $20 Halogen work light from Lowes.  It is 250 Watts and works fine.  That pulls about 20 amps....so close enough to the recommended 25 amps.
• You can do the test and need a VOM.  Here is the revisions or the simplification. Obviously FILL the batteries properly with DI water...
• After the House is charged.  Turn on a TV or fans or whatever and let the inverter run.  When the meter reads around 12.7 Volts....STOP.  This is NOT precise...all you are doing is knocking OFF the surface charge. STOP...turn OFF the House Disconnect.  Remove the Jumpers and measure the batteries....WRITE IT DOWN....this is the "presumed SOC" or should be in the 6.37 VDC range....if it is LOWER...then you KNOW that they will NOT recharge to 100%...but how much and you can improve them by exercising....how much?  that depends..... 
• NOW...make sure a solar panel is covered or the fuses in the controller or pull unscrew the HOUSE terminal and remove the battery lead in the controller
• I would turn off at a power strip or unplug all TV, Satellites or DVD or receivers or whatever....so you ONLY had 250 Watts on the inverter.
• NOW...I monitor or write down the voltage on the meter and the VOM reading on the Batteries about every 15 minutes and monitor the drain.
• When you get to about 11.9 or  12.0 on the VOM, you will be close to 50%
• THEN kill the load.  Turn OFF the House Battery Switch.  Pull the Jumpers from the House batteries and let them SIT.  Wait maybe 15  to 30 minutes.  THEN measure the individual batteries.  At that point, I use my Hydrometer and also measure the Specific Gravity....
• THEN WRITE DOWN THE VOLTAGE.  Use the CHART.  That tells you HOW LOW they were depleted.  ALSO record the TIME....or minutes that it took.
• NOW....reconnect the Jumpers.  Turn on the Disconnect.  Charge THE BATTERIES UP.....now REPEAT THE TESTREPEAT 2 more times....
• At the END...you SHOULD have if the Batteries are GOOD or 100%, the 6.37 VDC after the final recharge (after knocking off the surface).  IF NOT....then the rule of thumb is....80% SOC or better....LIVE WITH IT...70% or SO....MIGHT need to Budget for new ones.... 50 - 60%....you have an issue...
• THE GOOD THING....the Trojans are the most ROBUST and hardest to "kill by neglect".  

That's how you do it.  HOW, as to "will they make it trough the night....that depends.  MY EXPERIENCE...as well as many others here.  A GOOD (90% or so SOC) bank of 4 will get you easily through the night with a Res Refer set in ECONOMY and LED's in the MH and NOT running the TV's or assuming you did a full charge before quiet hours ended or at bedtime.  The Batteries will probably be around 60%....or maybe a smidge higher.  Depends on the heating needs...

Here is a REALLY TECHNICAL ANSWER...  Using the 20 amp trouble light....and draining the batteries to 6.12 (the BOUNCE BACK or RECOVERY VOLTAGE), which is 60%...  Now you have pulled 40% of the Amp Hours or "MINUTES".  A bank of four....has a 20 Amp capacity of 1,118 Minutes.  SO, when they are at 6.12 VDC, they have used up 40% of their capacity.  That is 447 minutes.  The Inverter STEALS 5%...so that is 425.  Divide that by 60...7.07 or round to SEVEN HOURS...

ALL of this is theoretical...  THE MAIN THING TO KNOW.... what is the SOC of my bank...after I quickly KNOCK OFF the surface and the reading, after pulling the Jumpers and they are fully charged and such....what is the VOLTAGE.  If it is around 6.37, then the Magnum should be reading around 12.7.  DO NOT be surprised if the Magnum is reading 12.5 or so....you NEED to know the accuracy or the correlation between what the BATTERIES are reading with a VOM and what the Magnum says.

That's it.... 

LifeLine Testing.pdf

[Tom Cherry]

26 minutes ago, 96 EVO said:

A few hrs of equalize charge would probably do them good as well!

I take my sealed chassis batteries out of the loop before I equalize my house bank.

BEN,

Trojan tech support says for OUR MOTOR HOMES...where we usually keep a high quality 3 phase charger/inverter on the bank......then NEVER, NEVER...unless the batteries are at getting weak or there are major differences....in a battery or between batteries........then EQUALIZE....  This is sort of a LAST RESORT. 

IF you stay plugged in....then they recommend the PERIODIC EXERCISING.

NOW....if you don't....and after you have exercised them....and they still are a bit "low"   THEN if the Specific Gravity is way different from cell to cell in one battery or the battery voltages are way different. THEN and ONLY THEN, equalize.  There is a page in the Manual that goes into this.

Trojan says to take that with a grain of salt...that not EVERY person has a MH like we do....You can read the specifics of the variation...but remember....if you keep the batteries charged....then test them....and if they then FAIL, then and ONLY THEN...should your Equalize.

They say that periodic equalization, when NOT needed, actually decreases the battery life. 

This is based on several phone calls with different tech support.  Magnum is more of a SOCK IT TO THEM Equalization vendor...but NOT Trojan. 

Technically, equalizing an AGM or a SEALED battery is the last resort...as you will NEVER, EVER (unless you drill or remove the covers) be able to ADD BACK THE LOST LIQUID....

[waterskier_1]

50 minutes ago, Tom Cherry said:

Rick is correct.

BUT, to answer your question....here is what is in the files.... READ ON AFTER THE LINK

When I wrote this and it needs a little revision, it was very general.  BUT, here is how your determine how good your Trojan's are....and how much capacity you have.

• FIRST, having them load tested is a waste of time.  Lifeline AGMs and Trojan's manuals both, I think, say...  LOAD TESTERS WILL NOT WORK on Deep Cycle. I printed out the Lifeline page 22 on how to TEST.  It is the best that I have seen.  YES, that is for an AGM, but it is applicable to Flooded...so it works for your batteries.....see the file page that I is a PDF
• Basically, the Trojans need to be exercised, drained to approximately 50%, about every 6 - 9 months.  That procedure is in the Battery 101 paper.  However, here is a little more "info" that I will add.
• The best device to run them down is a $20 Halogen work light from Lowes.  It is 250 Watts and works fine.  That pulls about 20 amps....so close enough to the recommended 25 amps.
• You can do the test and need a VOM.  Here is the revisions or the simplification. Obviously FILL the batteries properly with DI water...
• After the House is charged.  Turn on a TV or fans or whatever and let the inverter run.  When the meter reads around 12.7 Volts....STOP.  This is NOT precise...all you are doing is knocking OFF the surface charge. STOP...turn OFF the House Disconnect.  Remove the Jumpers and measure the batteries....WRITE IT DOWN....this is the "presumed SOC" or should be in the 6.37 VDC range....if it is LOWER...then you KNOW that they will NOT recharge to 100%...but how much and you can improve them by exercising....how much?  that depends..... 
• NOW...make sure a solar panel is covered or the fuses in the controller or pull unscrew the HOUSE terminal and remove the battery lead in the controller
• I would turn off at a power strip or unplug all TV, Satellites or DVD or receivers or whatever....so you ONLY had 250 Watts on the inverter.
• NOW...I monitor or write down the voltage on the meter and the VOM reading on the Batteries about every 15 minutes and monitor the drain.
• When you get to about 11.9 or  12.0 on the VOM, you will be close to 50%
• THEN kill the load.  Turn OFF the House Battery Switch.  Pull the Jumpers from the House batteries and let them SIT.  Wait maybe 15  to 30 minutes.  THEN measure the individual batteries.  At that point, I use my Hydrometer and also measure the Specific Gravity....
• THEN WRITE DOWN THE VOLTAGE.  Use the CHART.  That tells you HOW LOW they were depleted.  ALSO record the TIME....or minutes that it took.
• NOW....reconnect the Jumpers.  Turn on the Disconnect.  Charge THE BATTERIES UP.....now REPEAT THE TESTREPEAT 2 more times....
• At the END...you SHOULD have if the Batteries are GOOD or 100%, the 6.37 VDC after the final recharge (after knocking off the surface).  IF NOT....then the rule of thumb is....80% SOC or better....LIVE WITH IT...70% or SO....MIGHT need to Budget for new ones.... 50 - 60%....you have an issue...
• THE GOOD THING....the Trojans are the most ROBUST and hardest to "kill by neglect".  

That's how you do it.  HOW, as to "will they make it trough the night....that depends.  MY EXPERIENCE...as well as many others here.  A GOOD (90% or so SOC) bank of 4 will get you easily through the night with a Res Refer set in ECONOMY and LED's in the MH and NOT running the TV's or assuming you did a full charge before quiet hours ended or at bedtime.  The Batteries will probably be around 60%....or maybe a smidge higher.  Depends on the heating needs...

Here is a REALLY TECHNICAL ANSWER...  Using the 20 amp trouble light....and draining the batteries to 6.12 (the BOUNCE BACK or RECOVERY VOLTAGE), which is 60%...  Now you have pulled 40% of the Amp Hours or "MINUTES".  A bank of four....has a 20 Amp capacity of 1,118 Minutes.  SO, when they are at 6.12 VDC, they have used up 40% of their capacity.  That is 447 minutes.  The Inverter STEALS 5%...so that is 425.  Divide that by 60...7.07 or round to SEVEN HOURS...

ALL of this is theoretical...  THE MAIN THING TO KNOW.... what is the SOC of my bank...after I quickly KNOCK OFF the surface and the reading, after pulling the Jumpers and they are fully charged and such....what is the VOLTAGE.  If it is around 6.37, then the Magnum should be reading around 12.7.  DO NOT be surprised if the Magnum is reading 12.5 or so....you NEED to know the accuracy or the correlation between what the BATTERIES are reading with a VOM and what the Magnum says.

That's it.... 

LifeLine Testing.pdf 22.68 kB · 0 downloads

Tom,  

Load Testing does work, and you included a document describing how to perform such a test.  I think maybe you meant that the typical Carbon Pile Load Tester used to test Automotive Starting (as distinguished from Deep Cycle) batteries will not work.  That device is designed to present a high load for a short period of time, simulating an engine starter.  The referenced procedure from Lifeline is what I recommend for all Lead Acid (Flooded or AGM) Deep Cycle batteries.  I don't recommend following your procedure of guessing where 50% is (11.9 or 12.0 or ???).  Also, the first 50% time does not necessarily represent the last 50% time.  If you follow the Lifeline procedure referenced, you discharge to 10.0 volts.  This is their definition "battery depleted" and what they use to rate their battery capacity.  Also, a constant current discharge is needed.  I agree with you that Halogen Shop light, on a "light dimmer" so they can be adjusted for precisely the current (25 Amps in this case) is achieved, but 250 Watts won't do the job.  I used a 400 Watt adjusted for the requisite 25 Amps.  To perform this test, you must change your low voltage cutoff on your inverter, since you want to discharge to 10.0 Volts which is lower than most have their invert set (typically 11.0-11.5 volts).  This is ONLY for this special case load test.  Now the 10.0 volts is special - it is the voltage UNDER 25 Amp Load, that represents a full depleted battery.  This is NOT the voltage you would read if you were to let the battery set.  Lifeline developed this test so you don't have to go through all the wait for surface charge, etc.  Speaking with the engineers, they acknowledge that this voltage is different that what you would read with the battery resting.  But this is a special load test.  It must be performed at 25 Amps to be valid.  A different discharge current (i.e., 20 Amps) would yield a different end voltage.  Depending on how close your inverter can maintain the output voltage with varying input battery voltage (it will vary from around 12.7 or so all the way down to 10.0 volts), it may not matter what you use as a load.  If you are performing this test without an inverter (an inverter is not necessary to to load test batteries), you would have to be more careful what you used as a load, since many resistive loads will cause the current to drop as the voltage drops (E=I*R) so incandescent bulbs don't work well).  You will time the load test.  Then compare the time it took to reach 10.0 volts to the rated time at 25-Amp discharge.  The ratio of these times will provide the percentage of battery capacity.  Note this is not remaining capacity, or used capacity, but the total capacity of the battery.  

This test will NOT calculate any voltage or Depth of Discharge or State of Charge Charts.  It is solely used to determine the condition of the battey.

Let me know if I can answer questions.  

  -Rick N.

1 hour ago, Tom Cherry said:

BEN,

Trojan tech support says for OUR MOTOR HOMES...where we usually keep a high quality 3 phase charger/inverter on the bank......then NEVER, NEVER...unless the batteries are at getting weak or there are major differences....in a battery or between batteries........then EQUALIZE....  This is sort of a LAST RESORT. 

IF you stay plugged in....then they recommend the PERIODIC EXERCISING.

NOW....if you don't....and after you have exercised them....and they still are a bit "low"   THEN if the Specific Gravity is way different from cell to cell in one battery or the battery voltages are way different. THEN and ONLY THEN, equalize.  There is a page in the Manual that goes into this.

Trojan says to take that with a grain of salt...that not EVERY person has a MH like we do....You can read the specifics of the variation...but remember....if you keep the batteries charged....then test them....and if they then FAIL, then and ONLY THEN...should your Equalize.

They say that periodic equalization, when NOT needed, actually decreases the battery life. 

This is based on several phone calls with different tech support.  Magnum is more of a SOCK IT TO THEM Equalization vendor...but NOT Trojan. 

Technically, equalizing an AGM or a SEALED battery is the last resort...as you will NEVER, EVER (unless you drill or remove the covers) be able to ADD BACK THE LOST LIQUID....

I think there may be new information on equalization.  Trojan now states "Equalizing should be performed when a battery is first purchased (also called a freshening charge) and on a regular basis or as needed. How often your battery will require an equalization charge will vary depending on your application."  You will need a way to measure Specific Gravity accurately.  Trojan states "it is time to equalize if the measured specific gravity (SG) values are below manufacturer’s recommended values after charging (recommended value for Trojan deep cycle batteries is 1.285 +/- .007 at 80º F (27º C)).

Personally, I never equalized.  If you choose to, disconnect the coach from the batteries and charger.  The equalization voltage is high enough it may cause damage to sensitive electronics and other devices.  Check with your manufacturer for the correct equalization voltage - Trojan is 16.2 volts for their 12-volt flooded cells.  Make sure your inverter/charger is properly set for this voltage.  Again, you will need to monitor the Specific Gravity every hour.  Trojan states "Equalization is complete when specific gravity values no longer rise during the gassing stage." 

The key to this is to get an accurate Specific Gravity tester, one that can resolve measurement to 0.01.  

  -Rick N.

[96 EVO]

Yeah, I bought 'quality' Rolls batteries!

They don't mind you equalizing their batteries!

[Tom Cherry]

3 hours ago, waterskier_1 said:

Tom,  

Load Testing does work, and you included a document describing how to perform such a test.  I think maybe you meant that the typical Carbon Pile Load Tester used to test Automotive Starting (as distinguished from Deep Cycle) batteries will not work.  That device is designed to present a high load for a short period of time, simulating an engine starter.  The referenced procedure from Lifeline is what I recommend for all Lead Acid (Flooded or AGM) Deep Cycle batteries.  I don't recommend following your procedure of guessing where 50% is (11.9 or 12.0 or ???).  Also, the first 50% time does not necessarily represent the last 50% time.  If you follow the Lifeline procedure referenced, you discharge to 10.0 volts.  This is their definition "battery depleted" and what they use to rate their battery capacity.  Also, a constant current discharge is needed.  I agree with you that Halogen Shop light, on a "light dimmer" so they can be adjusted for precisely the current (25 Amps in this case) is achieved, but 250 Watts won't do the job.  I used a 400 Watt adjusted for the requisite 25 Amps.  To perform this test, you must change your low voltage cutoff on your inverter, since you want to discharge to 10.0 Volts which is lower than most have their invert set (typically 11.0-11.5 volts).  This is ONLY for this special case load test.  Now the 10.0 volts is special - it is the voltage UNDER 25 Amp Load, that represents a full depleted battery.  This is NOT the voltage you would read if you were to let the battery set.  Lifeline developed this test so you don't have to go through all the wait for surface charge, etc.  Speaking with the engineers, they acknowledge that this voltage is different that what you would read with the battery resting.  But this is a special load test.  It must be performed at 25 Amps to be valid.  A different discharge current (i.e., 20 Amps) would yield a different end voltage.  Depending on how close your inverter can maintain the output voltage with varying input battery voltage (it will vary from around 12.7 or so all the way down to 10.0 volts), it may not matter what you use as a load.  If you are performing this test without an inverter (an inverter is not necessary to to load test batteries), you would have to be more careful what you used as a load, since many resistive loads will cause the current to drop as the voltage drops (E=I*R) so incandescent bulbs don't work well).  You will time the load test.  Then compare the time it took to reach 10.0 volts to the rated time at 25-Amp discharge.  The ratio of these times will provide the percentage of battery capacity.  Note this is not remaining capacity, or used capacity, but the total capacity of the battery.  

This test will NOT calculate any voltage or Depth of Discharge or State of Charge Charts.  It is solely used to determine the condition of the battey.

Let me know if I can answer questions.  

  -Rick N.

I think there may be new information on equalization.  Trojan now states "Equalizing should be performed when a battery is first purchased (also called a freshening charge) and on a regular basis or as needed. How often your battery will require an equalization charge will vary depending on your application."  You will need a way to measure Specific Gravity accurately.  Trojan states "it is time to equalize if the measured specific gravity (SG) values are below manufacturer’s recommended values after charging (recommended value for Trojan deep cycle batteries is 1.285 +/- .007 at 80º F (27º C)).

Personally, I never equalized.  If you choose to, disconnect the coach from the batteries and charger.  The equalization voltage is high enough it may cause damage to sensitive electronics and other devices.  Check with your manufacturer for the correct equalization voltage - Trojan is 16.2 volts for their 12-volt flooded cells.  Make sure your inverter/charger is properly set for this voltage.  Again, you will need to monitor the Specific Gravity every hour.  Trojan states "Equalization is complete when specific gravity values no longer rise during the gassing stage." 

The key to this is to get an accurate Specific Gravity tester, one that can resolve measurement to 0.01.  

  -Rick N.

First…yes, if you start out, which I did not want to go that deep into, you can calculate the exact time for any depletion or run down.  It is in my Post.  The 25 Amp hour rating for a Trojan T105 is 447 minutes.  So if you reduce the amperage to 20 amps, that would be, I think a 20% increase…I MIGHT have used a different ratio. But then you would expect 536 minutes until full or zero depletion.  OK…say you want to stop at 60%.  Then 40% of 536 is 215.  You have two in series and two of those two in parallel,..thus you double the 215…or 430.  But you have to knock off 5% that the inverter uses….or 408 minutes.  My example was a 25% increase…so the logic is the same….just calculating the time.  Bottom line.  If you had a PURE 25 amp load, allowing for the 5% inverter parasitic drain, then the minutes until that SOC, based on the Rebound voltage is exactly how Trojan says to do the calculation.  I bounced this off others and yes, you can calculate how LONG the battery should last with a fixed or given load, within the manufacture’s parameters.  Trojan may use a % of capacity where LifeLine defines it.

Second.  Yes.  I did READ the passages that you posted.  I started to copy….but in reality, Trojan frowns HIGHLY and does NOT, on the phone, recommend, for our operating conditions where we keep a float charge on, EQUALIZATION.  They also commented that Magnum was “not correct” and that we, MH owners, would shorten the life.  NOW….are those tech support persons still there?  I didn’t record or get their names.

Bottom line, when one doesn’t have a shunt system, the  following Trojan’s advice and knowing the SOC of their battery is the best advice.

YES…a Hydrometer is great….and there are good ones.  But measuring voltage is easier and more accurate.  The OP wanted to know HOW to judge and doesn’t presumably have the Shunt system.

My advice was to exercise and maximize the batteries and get them back into shape.  Then measure and check the SOC….which is easy to do with nothing but a VOM…and then have him the “general” info on how folks without a Shunt system, but years of experience usually judge them.

Hope this explains the logic and also  my response to Ben.  As usual, when we have input  from a Manufacturer, we pass it on…plus look at what they publish as well as talk about why not one size fits all.  Magnum says their manuals are “guidelines” and the higher levels of understanding would be difficult to write or convey to their average customer…

 

[waterskier_1]

20 minutes ago, Tom Cherry said:

First…yes, if you start out, which I did not want to go that deep into, you can calculate the exact time for any depletion or run down.  It is in my Post.  The 25 Amp hour rating for a Trojan T105 is 447 minutes.  So if you reduce the amperage to 20 amps, that would be, I think a 20% increase…I MIGHT have used a different ratio. But then you would expect 536 minutes until full or zero depletion.  OK…say you want to stop at 60%.  Then 40% of 536 is 215.  You have two in series and two of those two in parallel,..thus you double the 215…or 430.  But you have to knock off 5% that the inverter uses….or 408 minutes.  My example was a 25% increase…so the logic is the same….just calculating the time.  Bottom line.  If you had a PURE 25 amp load, allowing for the 5% inverter parasitic drain, then the minutes until that SOC, based on the Rebound voltage is exactly how Trojan says to do the calculation.  I bounced this off others and yes, you can calculate how LONG the battery should last with a fixed or given load, within the manufacture’s parameters.  Trojan may use a % of capacity where LifeLine defines it.

Second.  Yes.  I did READ the passages that you posted.  I started to copy….but in reality, Trojan frowns HIGHLY and does NOT, on the phone, recommend, for our operating conditions where we keep a float charge on, EQUALIZATION.  They also commented that Magnum was “not correct” and that we, MH owners, would shorten the life.  NOW….are those tech support persons still there?  I didn’t record or get their names.

Bottom line, when one doesn’t have a shunt system, the  following Trojan’s advice and knowing the SOC of their battery is the best advice.

YES…a Hydrometer is great….and there are good ones.  But measuring voltage is easier and more accurate.  The OP wanted to know HOW to judge and doesn’t presumably have the Shunt system.

My advice was to exercise and maximize the batteries and get them back into shape.  Then measure and check the SOC….which is easy to do with nothing but a VOM…and then have him the “general” info on how folks without a Shunt system, but years of experience usually judge them.

Hope this explains the logic and also  my response to Ben.  As usual, when we have input  from a Manufacturer, we pass it on…plus look at what they publish as well as talk about why not one size fits all.  Magnum says their manuals are “guidelines” and the higher levels of understanding would be difficult to write or convey to their average customer…

 

Tom, I'll mention a couple of misconceptions it looks like you have.  First, the discharge time is NOT linear to discharge rate.  This is to say that a discharge of 50 Amp is not double the time that a discharge of 25 Amps.  Or, at a more extreme, the time to discharge at 1000 Amps is not 100 times the time do discharge at 10 Amps.  Most all documentation will explain this.  Yes, that might be getting in the weeds, and you may be using a rough estimate to get there, but why not use the proper methodology.  The second point is that the discharge curve at the same current is not linear.  That is to say that the amount of time it takes to discharge 10% from 100% to 90% is not the same time it takes do discharge 10% from 20% to 10% of battery capacity.  Nor is the top 50% time the same as the bottom 50% time.  Sure, your methodology does provide some level of condition, within maybe 20% or actual value, which is plenty good to sort out dead or very bad batteries.  But it does not yield accurate (or even as accurate as we can reasonably get in a field test on our coach batteries) result.  

A clarification on the procedure.  If you do decide to use the inverter to drive a 110 VAC load, then you measure the INPUT to the inverter, not some output which might include parasitic loads (and inefficiencies of the inverter itself).  You would (or should) measure the TOTAL current being drawn from the battery.  That should make sense?  I did this with a shunt in the negative battery lead, but you could simply use an accurate DC clamp-on Ammeter.  This can be done with either a direct DC Load or using the inverter to supply an AC load.  The idea is to create a 25 Amp load on the battery - without regard as to what might be causing it.  Again, I want to stress this is a LOAD TEST to determine the Capacity of the battery.  This is not designed to relate some state of charge to voltage or an intermediate % of charge.  

Okay, I know you have talked to a lot of technical people at a lot of manufacturers.  I don't have that time to call all of them.  I must rely on Manufacturer's Published Documentation, not hearsay.  Let me be clear, I do not doubt in the least that you were told many things.  But I have been too, and sometimes they are completely wrong, or the question or answer misunderstood, because the other person "thinks" he knows what is being asked/answered.  I propose that if the reader finds a totally opposite direction from tech support than what is published, then it's up to the reader to investigate further.  I have no doubts that, regarding equalization, there are many misused procedures causing problems.  Also, not all battery chargers are created equal.  That is why I look at the specified values and outcomes, versus just turning any charger loose in Equalize Mode.  Not only can it cause harm to the batteries, but also anything that happens to be on the wire when the charger applies 16.2 or more volts.  I suppose if I were asked a general question, I would respond, as I did, and state that I do not recommend using it.  I have used it, to attempt to resurrect suspected bad batteries, but ALWAYS isolated from the coach (i.e., removed from the coach).  That said, what I posted is what the manufacturer has published, and not hearsay, the reader can take that or leave it.

 Another thing - voltage is used only for a convenient way to "guesstimate" the SOC or charge of a battery.  It is no way directly related, mathematically, to the condition of a battery.  The voltage, which will vary by battery manufacturer, is obtained by experimental measurement.  One should never use voltage as a fine measurement of the condition of a battery.  The charts are only give as a reference for those who have no other way of estimating the condition.  It is kind of like using a wind sock to gauge the wind speed.  Yes, there is a relationship to the wind sock and air speed, but it is derived by observing the wind sock while the wind speed is measured by a more accurate, precise and repeatable means, typically an anemometer.  Just like battery condition is measured by hydrometer.  Voltage may be easier just like glancing at a wind sock is easier, but there is no way either is more accurate.

In the future, when you gain knowledge of Lithium batteries, you will realize that voltage doesn't provide any significant indication of battery state of charge.  Lithium batteries vary less than 0.01 volts over 10% charge and some are less than 1.0 volts difference between 20% and 90% capacity.  The differences can be easily lost in wiring losses when we are talking 100's of Amps (which many systems require - remember, that is only 10's of Amps at 110 VAC.  Everyone should be migrating away from using voltage to determine a "value" of battery condition.  It can be used for comparison purposes, like I now have more charge in my battery at 12.5 volts than I did before charging when I read 11.9 volts, but one should refrain from attaching absolute percentages to those readings, especially, as you have pointed out, that the voltage reading are only valid for a specific manufacturers' specific chemistry, and in the case of lead acid, only after the battery has be disconnected from any charge/discharge source, and surface charge has had time to dissipate.  Not many of us want to remove the cables from our batteries and wait an hour or more to determine the state of charge of our batteries.  Especially since there is an economical, easy to use, alternative. 

Sorry about likely getting into the weeds on this.  

  -Rick N.

[96 EVO]

Wow, that's deep!

I'm going to tell the OP (Mike), what I use when exercising my house bank.

I use my coffee maker on inverter. It uses a carafe, without a hot plate, and according to the Magnum remote, draws about 90A DC from the batteries while brewing.

With about a half hour rest between pots for the inverter to cool down, my batteries after sitting on float charge for weeks, will make 3 or 4 pots before the batteries are showing 12.0V (rested).

After charging them back to full charge, then repeating this process 3 times, they are good for 7 or 8 brews before the bank gets to 12V (rested)!

Very unscientific, but it works for this hillbilly 😁!!

 

[Rikadoo]

Hello Mike, so in answer to your vacume cleaner draw, yes depending on the mfg. i am surprised just how much they do draw. Couple months ago a customer of our wanted to outfit there work van to run there vacumes when there on the job site, i thought… NP! Well i was wrong an infact recommended a generator instead. There vacumes are commercial style and the current they consume is amazing, originally i tried a 2K watt inverter and it went to immediate overload alert, i then used a 3k inverter however even though it got it running the draw from the battery was crazy. I believe it will depend on the type of vacume you are using will depend on current draw. I purchased a ninja type vacume for my rig an its ok, however if i use the wifes Kirby its a different story.

[George L]

I would like to thank all of you for bringing up the the conditioning of our batteries. We as full timers do not nessasarily think about it, well, at least I did not. I will now start periodically conditioning my batteries. 

[96 EVO]

What I've been doing lately is starting 3 days before a boondocking trip, cycling the batteries each day.

This way my batteries are holding good capacity right from the first day.

If no boondocking trips planned, I'll cycle them every couple of months. The rest of the time they are float charging.

[Georgia Mike]

Lots of great information here. The vacuum cleaner I used was the one that came with the Motorhome installed under the sink cabinet. I plan on checking the house batteries thoroughly and I ordered a deep cycle hydrometer. In the mean time I plan on running down the batteries to just under 12.0 and do this a few times. I can use my refrigerator as a test it draws 11 amps and is connected directly to the house batteries so I can leave the main disconnects off, turn off my solar panels and monitor the voltage and amp draw from my shunt meter and solar voltage meter. I will time how long it takes to deplete the batteries and hopefully it will improve with each cycle. In the two years I have owned this Dynasty i never have really exercised the batteries at all. The solar always keeps it fully charged and we never dry camp so I can see why they need to be drawn down and used like they where intended.