Abila: How to charge AMG batteries

This discussion was created from comments split from: Charge rate for new Agm batteries.

• Posts: 1Registered Users
I have 4 x 225 amp/hr batteries that are AMG how should I be charging them without solar panels. I am using a 12 volt charger for AMG batteries.
Welcome to the forum Abila. I have moved your question to your own thread to keep things from getting confused.

I think you have a typo? AMG or AGM (absorb gas matt) battery?

Assuming AGM, the nominal method is to charge at 5% to 13% rate of charge (i.e., 225 AH * 0.10 = 22.5 Amps nominal charging current). And charge until the charging current falls to ~2% or 1% of rated capacity (225 AH * 0.01 = 2.25 amps) while charging at 14.2-14.4 volts (if charger has settings, this is for "sealed" lead acid batteries).

Depending on how big your battery charger is, it will take around 2-5+ hours for charging a discharged battery (bulk stage charging--basically full rated charger current) plus another ~2-6 hours of charging for Absorb charging (holding voltage at ~14.2 to 14.4 volts).

AGM batteries have very low self discharge current, and need to be recharged every ~3-6 months (flooded cell batteries have higher self discharge and need to be recharged every ~30 days). Letting lead acid batteries set for too long at less than full charge (under ~75% state of charge), the batteries will quickly sulfate and die.

AGM batteries are also very sensitive to high charging voltages and over charging.... If charged >~14.4 volts, they will gas and overheat. Once they gas (or overheat the catalyst, if present), they will have lost much of their life.

Once charged, either disconnect all loads, or hold them at "float voltage" of ~13.2 to 13.6 volts.

This is all at room temperature... Lead Acid batteries last longer if stored at cool temperatures (room temperature or less). If stored in a hot location, they will "age" faster (the rule of thumb is for every 10C/18F over room temperature, they will age 2x faster).

As always, details matter. Have you searched for the brand/model of your batteries and see if you can find a manual or charging instructions? The above is a generic starting point... Always follow mfg. instructions (especially if you want the warranty to honored).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset