Charging a Miata AGM Battery Question

[POS Racing]

OK lets say hypothetically that the trunk on a 2002 Miata was inadvertently left open for a considerable amount of time. The car will start but seems to not be turning over at full speed.

How long would you want to charge it to get it back up to full capacity??

BTW. I've hooked my 2 amp charger to it.

Thanks!

[onething]

JUST
DRIVE
IT!

[Treibenschnell]

I agree... if it starts then a good half hour drive or so should help.

[POS Racing]

So let's say it's going to sit in the garage overnight, would an overnight charge bring it back to 100%??

Hey I found what I was looking for on Miata.net! I remebered reading something about charging the AGM battery!

One of the differences with the AGM battery compared to the wet-cell battery is the recharge rate. That is, how fast you can put energy back into the battery. With a wet-cell battery you can "quick charge" it at about 20 amps or more. Usually this is when you would boil the electrolyte right out of the battery. The AGM batteries require a lower charge rate, for a longer time period. If your battery will not crank the engine, you should charge the battery at a rate of 1 amp or less for 18-24 hours. If you try and charge it like a wet-cell battery, you will destroy the battery.

Linky!

[Kiliwizz]

Having destroyed a westco battery by completely discharging and then jump starting the car (x4 ish) I know the truth of what is written...

Ideally, you need a constant current then a constant voltage charger, not just a constant current one. But trickle charging is ok as long as you frequently monitor the voltage.

Look at the AGM section here to see how they charge.

Also, don't bring this subject up on the board, unless you want to be nagged, insulted and patronised....(grr)

[channelmaniac]

Also, don't bring this subject up on the board, unless you want to be nagged, insulted and patronised....(grr)

Sounds like the voice of experience!

I put the charger on mine long enough to get it charged up where it'll start the car then drive it for a long roadtrip. More fun and it's never failed to fully charge the battery.