Chassis FLA Batteries and House AGM Batteries, Using same charger, Is this OK?

[Bill R]

I have searched the Monacoer's site, and I am sure this has already been addressed, but I could not find a thread.

When we bought our coach it came with 4-6V AGM House batteries and 2-12V AGM Chassis batteries.  All batteries were purchased in beginning of 2018.  The house batteries seem to still be giving good performance.  We do not boondock, so house batteries serve as interim power during travel days.   However, the chassis batteries are needing to be replaced, and this time I am considering FLA batteries.   

I have read other posts elsewhere that say the charging profiles are similar enough to use the same charger (Magnum ME2012) and this is fine.  

But I value this forum more highly.  So, is this ok or what are the concerns about FLA Chassis with AGM House using the same charger?

[Tom Cherry]

21 minutes ago, Bill R said:

I have searched the Monacoer's site, and I am sure this has already been addressed, but I could not find a thread.

When we bought our coach it came with 4-6V AGM House batteries and 2-12V AGM Chassis batteries.  All batteries were purchased in beginning of 2018.  The house batteries seem to still be giving good performance.  We do not boondock, so house batteries serve as interim power during travel days.   However, the chassis batteries are needing to be replaced, and this time I am considering FLA batteries.   

I have read other posts elsewhere that say the charging profiles are similar enough to use the same charger (Magnum ME2012) and this is fine.  

But I value this forum more highly.  So, is this ok or what are the concerns about FLA Chassis with AGM House using the same charger?

As my corporate lawyers always told me to say....IT DEPENDS.

Do you store the MH with power?  If so, is it 30 Amps so that your Magnum can charge properly?

Does your MH have a BIRD Module so that you get charging of BOTH banks while traveling or in the CG? (I have seen what I believe was the OEM charging circuit and I believe that the particular system was a BIRD). Your manual does NOT call out a BIRD type of charging....but says that your Alternator will charge the House during travel....but nothing about the reverse such as charging the Chassis while camping and on shore.

  Your manual also states that you should have STARTING ONLY for Chassis and DEEP CYCLE for House.  Are your Chassis AGM's actually STARTING or Deep Cycle.  Many folks have not been aware of that and we have all sorts of battery combinations where starting batteries were switched and also some are running the "Combo" which give poor service life.

Did you cycle and exercise the AGM's as you should with FLA as well once or more annually down to 50% so that they will deliver full power.  AGM and FLA will get lazy or take a "SET" if you don't do that.  Here is a file that goes into batteries....

MY GUT...and this is a personal opinion....but it is based on a lot of experience and reading and such....  AGM's for starting are not my choice.  AGM's are more persnickety and DO require a different profile than FLA.  If you properly configured, and Magnum can tell you....the ME2012 for AGM, then it should be OK.  The FLA's are actually MORE robust.  If you do NOT have a BIRD (in that your Chassis is NOT charged while camping or in storage), then I would go back to FLA's.  The way your system works, unless someone has modified it or added FULL BIRD capability is that when you DRIVE, you get SOME (the manual warns NOT TO try to recharge a depleted bank of House with your alternator as ugly things happen) charging from the Alternator to the House.  BUT, if you are running the Genny for AC as many of us do, then the Magnum is taking over and will probably work be OK for the AGM's.

For Storage, I would consider a stand alone 2 amp (maybe up to 3 A) plug in charger for the Starting.  That will keep the sealed FLA's happy.  Your need a MAINTAINER, not a cheap 6/12 charger.  The Maintainer will have a charging or maintaining circuit that tops off....like your Magnum does....and then quits.  The BETTER ONES...and they add years to FLA's is the one with a Desulfonation cycle. I use that on my wife's ATS (AGM) and my Vette (FLA) as needed when we are traveling.  Both batteries are several years old and still in great shape, based on my tests and measurement...maybe borrowed time....LOL

So....NO BIRD....then FLA but keep a charger or maintainer on the Chassis....or drive the MH a few hours every few months to recharge the Chassis.  You can (take this and study it) actually start the Genny every few months....put a jumper on the positives (House and Bank) and use the Magnum to charge both.  You can use the AGM setting as the FLA's are not as picky....and BOTH will be charged.  

I DO think that the older engines and alternators were NOT designed for and are not "NICE" to AGM's.  FLA's were more robust or less picky.  I also notice how the newer vehicles work (at least on my 2014 ATS and Yukon and 2016 Vette).  ALL those electrical systems are NOW....ON DEMAND.  I have a Volt Meter on each one or can call one up on the displays.  Sometimes it is flat 12.7 or so....other times....in the mid 13's and then sometimes in the low 14's.  I talked to the Caddy/GMC and Chevy techs.  That is NOW normal.  The electronics now are closer to our Magnums in that it senses Bulk, Absorb and Float needs.  The Cummins like you have as well as mine....always put out 13.8/.9....and I THINK that the AGM's when they are full charged don't like that.

SO....YES, based on my logic...and others might agree and I know some will disagree....I would go back to FLA's on the chassis.  BUT, when I needed new House....the Trojan T-105's (FLA) would be my choice.  That is how the electrical system and the Magnum was designed and you can do MORE damage with improperly charging (your situation) an AGM....than damaging a FLA.

Hope this helps....see what others say and do some research...but you should be OK...keep the Magnum set for AGM's.  Use the Jumper to charge, occassionally, if needed the new FLA's and then go forward.  BUT....buy the 950 CCA batteries...NOT THE CHEAPER 750...you will regret it....trust me...mine came with them and I upgraded and will never go back.

[Jdw12345]

I can’t give any real long term advice, other than we purchased our coach a little over a year and a half ago, it has 2 group 31 FLA chassis batteries that are 4 years old, I have 4 AGM Full River DC250 house batteries that are 9 years old, I have a zantrex 2012 inverter/charger set, to my understanding, correctly for the AGM’s charging profile, they seem to maintain a 13.4-13.8 when checked with a multi meter, the chassis batteries could probably withstand a higher voltage but I don’t believe that’s possible, with my setup. Fwiw.

Edited April 26, 2023 by Jdw12345

[TomV48]

"AGM's for starting are not my choice.  AGM's are more persnickety and DO require a different profile than FLA.  If you properly configured, and Magnum can tell you....the ME2012 for AGM, then it should be OK.  The FLA's are actually MORE robust."

I have contrary view.  I was so tired of FLA batteries that I had started with one auxiliary AGM the Blue Beer Can one in our first trailer as a stand alone in the bedroom to power my C-PAP.   I mixed FLA and AGM without a problem but as soon as the Blue Beer cans were full I pulled them off line.   Now ten or twelve years later that little puppy still holds a charge like new.    Same arrangement in our second trailer only TWO big Golf Cart batteries and the little Blue beer can as back up .

When We got this DP in the first of 2020, it had all Agm's.  Two big ones for the house and two Gr 31s for the chassis.  They all worked fine but they were really old.   I love the AGM.  But I love my LiFePo's more.  I put in LiFePo's for the house,  but the Chassis Batteries were still scary old, like ten years old,  so for peace of mind I decided that they needed replaced.   I found that Three of the highest CCA rated, Optima, Beer Can batteries fit in almost to a tee, where the two big Group 31 Agms had been and with more CCA.  I played with all sorts of really Expensive AGMs and found the most power for the money and square inches of battery tray available was the Optima

I was in a quandary to know how to charge them all when off grid.  House batteries charge using solar off grid and on hookup the Magnum,  was also set to charge LiFePo.  So I knocked out the boost relay/alternator cross feed to the house out.   I figure if I have to I can use big jumper cables where some rely upon the boost button,  I added a Renogy 40 amp DC-DC charger to the LiFePo's for the protection of the alternator and then strapped the Chassis batteries to them for cross charging/trickle charging,  with a Big old diode to cause a one way only charge and a half volt drop to not over charge the AGM chassis batteries. Thinking about replacing the cross feed diode with a simple 10 amp solar charger that will think LiFePo voltage is a solar source and then be a four stage charger specific to AGM chassis batteries.  10 amp PWM solar charger is actually half what I paid for that big old clunky Diode, and it mounts to the bulkhead easier.   That is so obvious but I never thought of it until I saw RV with Tito and he did it for his older Winnebago Gasser.  Still half of all I know about RVs came from YouTube.

[Bill R]

@Tom Cherry Thanks for the response.  Yes I do have a BIRD.  It is the bolt on MTO BIRD that must have been installed post manufacturing.  I do keep plugged in on 20A shore power while in storage.    I have had this coach for 1.5 years, but since then, I do exercise the house batteries every 3 months or so.  So there was already over 3 years service life on them, some abuse before I think, but still plan to keep exercising them.

You bring up a great point about if the starting batteries are Deep Cycle.  I looked up the specs, MARINE31DTMAGM, it does say they are deep cycle.  So these starting batteries may not have ever been exercised.  And they are not what the manual recommends.  Why would you want deep cycle for starting batteries?   Might explain why they are not lasting. 

So I will have Deep Cycle AGM for House and standard (not Deep Cycle) FLA for Chassis, and BIRD combining both banks while on shore, I believe I will be OK?  And I do have the PowerPulse for the batteries. 

FYI, when the House AGM's are exhausted, I will replace them with Deep Cycle FLA's.  So all this should be mute at that point.  But until then, it seems I should be good if I am correctly understanding your comments.

[96 EVO]

I would set the Magnum to AGM.

Even when (if) you change your chassis batteries to FLA, I'd leave it on AGM. (The chassis batteries can handle it).

[Gary 05 AMB DST]

I am a believer in keeping things the way they were from the factory. A lot of changes have been made electronically that the older MH's weren't designed for.

Gary 05 AMB DST

[Bill R]

@Gary 05 AMB DST The MSRP Sheet says the unit came with 4-6V Deep Cycle (not stated but I assume FLA) for the House and 2-12V Group 31 for the Chassis.  This is what I I plan to eventually be.  Transitioning first with 2 Group 31 Starting FLA batteries.  When the existing AGM Deep Cycle House batteries are exhausted, I will replace them with FLA Deep Cycle.  So back to factory for me as well.  I know this is all a personal choice with batteries.

[TomV48]

26 minutes ago, Bill R said:

@Gary 05 AMB DST The MSRP Sheet says the unit came with 4-6V Deep Cycle (not stated but I assume FLA) for the House and 2-12V Group 31 for the Chassis.  This is what I I plan to eventually be.  Transitioning first with 2 Group 31 Starting FLA batteries.  When the existing AGM Deep Cycle House batteries are exhausted, I will replace them with FLA Deep Cycle.  So back to factory for me as well.  I know this is all a personal choice with batteries.

That is definitely the old school GO TO.  And of course that is what my manual on our 05 AMB 34 shows, but they now make nice AGMs that will fit and for a long term investment, LiFePo's that will fit that four GC2 place.   Plus, if I never have to water another battery it will still be too soon.  They are even selling AGM/SLA batteries for most Automotive applications now too. There are probably four 12v AGMs out there that will fit the spot if GC2's in AGM are too hard to find. .  

[Tom Cherry]

22 minutes ago, TomV48 said:

That is definitely the old school GO TO.  And of course that is what my manual on our 05 AMB 34 shows, but they now make nice AGMs that will fit and for a long term investment, LiFePo's that will fit that four GC2 place.   Plus, if I never have to water another battery it will still be too soon.  They are even selling AGM/SLA batteries for most Automotive applications now too. There are probably four 12v AGMs out there that will fit the spot if GC2's in AGM are too hard to find. .  

YES.....  You NEVER have to water the AGM's.  GREAT.  BUT, if you don't take the time to EXERCISE them....and it is the SAME for an FLA, then your investment will have a shorter life....as in you may only get 6 years of life from a set of batteries that you paid 50% more for than FLA and if you properly maintained as in Exercising, them...and the maybe 10 minutes per cycle or less to fill them, then you will easily get 9 years.  What is your time worth.

Not to be critical...but AGM's are NOT bullet proof.  Quite the contrary.  Make a mistake or overcharge or totally run them down....they are more prone to damage.  BUT, if you maintain them, set up the charger properly and then exercise them, they will last as long as FLA's but not any longer but you DID NOT have to water them...

Call Trojan....ask them...

As to the automotive use of AGM's the Interstate distributor says that they switched back to FLA as they got limited life and their truck's charging systems were not designed for AGM and all they did was around town.  My wife's ATS has an AGM.  It has maybe 6 years on it.  I keep it topped off with a maintainer that will work for FLA and AGM.  If we don't drive enough (short stop and go trips) and no road trips, I can watch the voltage and it is really high.  SO, I either take a road trip or leave it on the tender. Interestingly....my 2016 Vette did not come with an AGM.  

Yes, I guess we are old school....but I am on my third bank....the Interstate's lasted maybe 4 years....I put in new Trojans circa 2021, but I really thought my 8 year old Trojan's were OK....really OK, but I decided to eliminate a variable for a low voltage hydraulic issue....and it was NOT the batteries.  I know folks here that have gotten 9 or more years or so....and they do the maintenance....and we run the Water Miser Caps....and we rarely add more than one ounce of Distilled Water per cell twice a year....but we EXERCISE...

That's what I have been told and read....and that is why I am old school....

 

[Bill R]

Thank you everyone for your comments.   I am confident from all comments that there is no issue using the Magnum set on AGM charging profile with combined AGM (house) and FLA (chassis) battery banks.

[96 EVO]

I don't really have a preference for house deep cycles Bill. I've been stuck in the dark ages with FLA in both of my coaches.

I know plenty of coach builders are now (many years) shipping with AGM.

I hear Entegra coach buries L16 AGM's so deep into a bay, that it's a nightmare just getting near them to replace. You wouldn't want to be adding water (they may even be laying on their sides).

With the cost of decent batteries up here in the great white north, and the pull out tray, I'll probably stick with FLA. 

When using the coach, gives me something to do while the wife is making lunch!  

[Pudgy Camper]

When you guys are talking about 'exercising' what are you referring too? I thought the inverter takes care of that in terms of float charge, desulfacation etc. I'm getting ready to get new batteries and want them to last as long as I can. I'm in AZ, and although my coach is stored indoors, it still gets quite hot during the summer months and its very hard on all batteries! 

[96 EVO]

Magnum inverter / chargers don't have an auto desulfacation mode.

Exercising is simply unplugging from shore, putting a decent load on your batteries till you get the bank down to about 50% (12.0V), resting, then charging them back up fully!

Do this about 3 times in row, and you will get better 'distance' from your batteries when you do need them!

Edited May 3, 2023 by 96 EVO

[Tom Cherry]

55 minutes ago, 96 EVO said:

Magnum inverter / chargers don't have an auto desulfacation mode.

Exercising is simply unplugging from shore, putting a decent load on your batteries till you get the bank down to about 50% (12.0V), resting, then charging them back up fully!

Do this about 3 times in row, and you will get better 'distance' from your batteries when you do need them!

Pulse Technology makes an inexplicable and reliable desulfonator. Many of us run them.  They were around $45.  They hook up to each set of 12.  Recommendation is 2 of them for a 4 bank set and one for the Chassis,  I have three running that way.  OK….the dirty little secret.

IF you follow your advice. Odds are you really don’t need desulfonizarion.  That comes direct from both Pulse and Trojan.  Batteries that are used and kept charged and exercised last typically last longer….and ….longer because the plates are cleaned,  

HOWEVER…I still think they are worth the investment and Pulse recommends putting one on an older set of four….then adding one when you get new ones .

Interesting thing….My Vette was cranked for the first time today in over 9 weeks.  I “put it to bed” before I had my shoulder replaced and left a desulfoonating maintainer on it.  No issue,  as I was driving I flipped through the digital gauges.  Running a shade under 13 VDC….so the battery is great.  That battery is an early 2016 OEM….so, imhave 7 years on it,  it was not cranked until late November, 2016 with a mid June build.

I’m happy….