Charging AGM Batteries

bdosborn wrote:
Does anyone have any information of what happens of you don't follow the recommened batery charging setpoints for an AGM? Do I cut my battery life in half? Does it blow up in the middle of the night? How do you test the battery for SOC and verify that the factory recommended charge setpoints are actually the best?

I'm the odd man out here battery-maintenance-wise, but have had very good luck with my battery maintenance routine.

We have had the same two 12V 100AH wheelchair AGM batteries in our motorhome for 7 years and they're still going strong. When the MH engine is running, these two AGMs are connected in direct parallel (via a heavy duty solenoid using silver alloy contacts) with the main wet cell chassis engine and the alternator. The chassis battery is about 5 years old.

When in storage during fall/winter/spring the AGMs get ~13.6-13.7 volts from our stock fixed voltage MH converter continuously. The chassis engine battery is continuously hooked up to a small multi-stage maintenance charger. During the summer when in storage the AGMs are disconnected from any charger much of the time so as to keep sulphation from being introduced by seeing a constant ~13.6-13.7 volts from the converter too long in warmer weather. The chassis wet cell battery remains constantly hooked up to the little multi-stage maintenance charger during the summer, too.

However, my batteries never sit much in a state of less than full charge and my AGMs are unusual in that they are wheelchair batteries that require floating at 13.5-13.8 volts - not 13.2 volts - so the fixed voltage converter does not harm them.

We don't drycamp longer than about 5 days at a stretch, so we merely hit the AGMs with some 14.X alternator volts once in awhile by idling the main engine for a bit and then following it up with 4-5 hours of converter voltage powered by a very small and quiet Honda generator - no solar. We can get by as much as around 3 days without idling the main engine or using the little Honda. We do keep the propane furnace cycling around 60-65 degrees all night most nights, too ... as well as using a no-heat no-steam CPAP machine every night. We have all LED lighting.

This simple system has worked well. Sometimes I think many RV folks make the whole battery maintenance thing too complicated. Just keep them always charged fully during extended storage without over-charing them and watch the charging time versus voltage in hot weather so as to keep from boiling them - or in the case of AGMs - to keep from vaporizing the water (which cannot be replaced) out of their one-way valves.