different size batteries in same bank

[bdavis441]

Let's say you have a battery bank with mismatched batteries. Example: one group27 and one group24, or one old and one new. If your charger is connected to the banks pos. line, how will it charge the batteries? My concern is it will charge the smaller battery fully and then proceed to charge the larger battery while cooking the fully charged smaller battery. Will a microprocessor controlled charger handle this. Or, if you have one battery going bad, will it affect the good ones?

[Roasting8]

The battery charger will overcharge the smaller battery and will not charge the bigger battery fully.

A bad battery, in a bank of good batteries, will draw down the other batteries. No matter how much you charge the bank, the bank will never get fully charged (you'll be lucky if the bank gets anything higher than the level of the bad battery). Please, just get rid of the bad battery.

[Steve]

If your batteries are hooked in parrallel they will not overcharge. The voltage will be the same across all the batteries and one cannot fully charge before another.

If one of the batteries is bad it will cause you to suffer battery lose when it is just sitting as the others in your bank will constantly trying to charge it. I think that having batteries in a large bank will help to keep any of the batteries from dying as long as you keep them charged.

** If you have a large bank of batteries, protect your investment and only use chargers that will automatically shutoff/trickle. **

BTW - I have three different sizes of batteries plus the engine battery hooked to my inverter/charger/transfer switch.

[Roasting8]

Sorry, I thought, for sure, that the smaller battery would start to boiling off before the big one.

[Les Lampman]

If the batteries are all connected together then the charger sees them as a "bank" and will respond to the voltage it sense from the bank and not an individual battery.

However...the charger doesn't know squat about each battery and any one of the batteries could be receiving much more current then is good for it (still charges to the correct voltage but does so in a way that damages it). Batteries have to charge from the surface of the plates in and thin plate batteries respond much differently then thick plate batteries.

For "best" performance (both charging and discharge) all the batteries in a bank should be of the same size and type. It's really even better if they're the same brand and age. That's what's "best" from a technical standpoint; lots of other things work and they're just fine if they do the job you want them to.