Charging agm battery bank

[Mat7783]

So I plan to buy a battery charger to charge probably 300AH battery bank and reading up on chargers. So Can these chargers handle 3. 100 AH batteries in parallel and reading like 10 hours to charge 100AH battery, or do I need to charge batteries separately? Please shed some light on this. I am not using solar at this time.

[JDOnTheGo]

Several connected batteries (a battery bank) is considered one large battery for this type of question. The entire bank is charged as one unit. A much more complicated answer is possible if looking at Lithium cells.

A good 3-4 stage RV style charger/converter is worth the money. Something like this. Be sure to select one that matches your battery bank voltage, chemistry, etc. The output rating (45 amp on that one) is related to how much power you require when in 'converter' mode (supplying DC power to the house) and the appropriate rate of charge for your batteries. There is an ideal (depending on battery chemistry, bank capacity, state of charge, etc.) but that involves a bit more information/design.

[Mat7783]

So if I go with a 400AH AGM bank, then I would probably need a 75amp converter to charge it from from let’s say 50 % depletion? Does that sound practical??thanks fir your input.

[JDOnTheGo]

This Trojan AGM battery spec sheet says maximum charge current is .2C (20-hour rate). Four of those batteries in a series/parallel config would give you a 12VDC bank of 440Ah. The maximum charge current for that bank would then be 88 amps.

The absorption rate of an FLA/AGM battery tapers off pretty quickly and is quite 'slow' as it nears 100% state of charge (SOC). So, a 'big' charger won't matter much once you get to ~70-80% SOC.

I haven't messed with FLA/AGM much since switching to Lithium and I am old & forgetful so hopefully someone will correct me if I got something wrong.