AGM Batteries

[Gros Ventre]

There have been several threads about these batteries. They are different than flooded cell lead acid batteries in construction and capacity. I have posted that the no load termianl voltage of a lead acid battery is ~13.2 VDC... I have now observed that my "spare" AGM battery (Over Thanksgiving last year I replaced the OEM battery because of some battery warnings on the road). My dealer later tested it and found it OK. So-o-o... I have a spare... Well over this year I have charged it up on several occasions and, while it goes up to 13.2 while charging, it quickly goes back down to 12.7 or 12.8 VDC and remains stable there... So-o-o... my conclusion is that Ford, in setting the system control voltage at 12.6 VDC, knew what they were doing. However, I still believe that every lead acid type battery needs an initial wetting down, low rate charge for long term good operation, regardless of where it settles out for a no load terminal voltage. Get an AGM specific charger for this, put your brand new AGM battery on the lowest rate charge (probably 2 amps) and let it charge to completion (likely some 10 hours).

PS The replacement AGM Battery (a NAPA battery) was run over Thanksgiving Weekend as it came from NAPA. On return home I put it on a long term, low amps charge. It took a bit over 10 hours for the charger to say the charge was complete. I have had no problems with this AGM battery since then. This includes going thru a Wyoming winter with temps down to -20º or -30ªF.

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[Calson]

Each type of battery has a maximum charge rate and that is why chargers have settings options. A lithium-phosphate battery can be charged at a much higher voltage and recharged much faster. The downside to these batteries is that they do not work well in very cold weather below 10 F degrees.

 

[Gros Ventre]

The low rate "wetting down" charge is to ensure all active materials are properly set up. You're not looking to max-out the charging rate, you're looking to allow all chemicals to be activated. Time charging at a low rate on initial wetting down is important for any lead acid type battery. The limits on charging rate for flooded cell lead acid batteries has to do with gas bubble formation in the active material. If the gas bubble formation proceeds too quickly it causes the plates to shed material slowly, shortening the battery life. I infer that there is a similar issue with AGM batteries since they're lead acid.

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