AGM Batteries storage maintenance charge

Auto discharge time/percentage is greatly affected by temperature

2oldman wrote:
0. AGMs hold a charge a long time. Maybe just check them now and then.

X2. I have two AGM 12V batteries in parallel and I just disconnect them from the trailer in October and they are still charged in May when I open the trailer again.

Ivylog wrote:
I would store them indoors and not worry about them...no charger:

I wouldn't. For three reasons:

Everybody needs a small battery charger from time to time.

A true "tender type" charger will drop down to OFF or float when they are fully charged and ramp up only when needed. If that is never needed during the storage time, it is little different than nothing being connected at all.

I think that checking the voltage of each battery after sitting for 3 months or so will give you a VERY rough idea of it's condition. If it is still 12.8 or above, I'd attach the tender for 48 hours or so and check again in another 3 months.

If less than 12.8, then I'd measure each one.

The most common automatic maintainers are rated at 2 amps and that is plenty for most people.

I would get 5 amps minimum if spending money.
I recommend Battery Tender brand and they have two at 5 amps depending if mounted or portable.

http://products.batterytender.com/Chargers/(shop around for better price)

I also agree with fully charge, disconnect and just let them sit.

I would store them indoors and not worry about them...no charger:

Rail Dawg wrote:
Two Trojan 6V AGM batteries in series (12v).

If we put them into 6 months storage fully-charged what would you recommend as the minimum amps for a charger/maintainer?

Thanks!

As a quick and dirty 3 amps if you keep them wired in series.
It's best to check what the manufacturer says though.

I think the OP meant what size of maintenance charger in amps, not how many amps should he be charging with. Each batt is full when it is accepting 0.5 amps or less for 12s but these are 6s, so 1.0 amp for the pair? So a 2 amp charger should do it.

Storage voltage should be temp adjusted from the battery spec storage voltage at 77F. Some AGMs have a higher spec voltage than others, so the AGM selection on any charger could be wrong for your AGMs or be right.

If you leave them with no wires on the terminals for 6 months they will be ok, but my AGM manual says after that long time you should do a full recharge routine and throw in an overcharge. It says you can go up to eight months without ruining my batts, don't know about Trojans if it is in their owner's manual

I would go for a small solar panel system myself. That way you end up with temperature compensated charging.

Forget amps. Constant current will get you into hot water, fast fast fast

With winter Reno temps. 13.2 volts would be a minimum and 13.6 a maximum.

Trojan issues specification for maintenance volts storage. Pay attention to temperature, 90 degree July is a long way from 0 degree February when the Washoe Zephyr is howling.

Easiest way is to buy a battery maintenance charger and slide the selector switch to AGM

0. AGMs hold a charge a long time. Maybe just check them now and then.