Hi Brad,
I use the Battery Minder. I have 4 flooded lead interstate batteries in series and parallel at 420 amp-hour each. Been on for 6 months with no issue.
I paid $169 which seems a little pricy, but got my recommendation on this forum. Haven't been disapointed.
Amazon.com: BatteryMINDer 244CEC1: 24 Volt- 1/2/4 AMP Battery Charger, Battery Maintainer, and Battery Desulfator - Designed for Trucks, Boats, RV, Generators : Automotive