Balance batteries before connecting in series

[Solar Bear]

Hello. I have two 12v 200Ah LIFEPO4 batteries that I want to put in series. They are both new and both have a current level of 13.27 in each battery. Since they are already balanced, do I need to also fully charge them before putting in series, or is it only important they they have the same voltage/charge? I don't have a battery charger (other than an old 12 volt 6 amp regular charger) to charge them before putting in series. However, once I have them in series, I can use my Growatt 3000 24V to fully charge them. Thanks.

 

[time2roll]

They might be OK and maybe not. 13.27 could still vary 10%+ in state of charge. One could go to overvolt protection if they are out of balance.

Running them up in parallel to 14.2-14.4 volts would get them in sync. Or if the balance is skipped.... the low battery could always be boosted as needed.

If the in service charging voltage is not too high it might be OK. Or it could work fine regardless. Watch it closely at the top of the first cycle.

 

[Solar Bear]

Thank you. Might try the parallel to sync.

 

[GSXR1000]

you can use your standard battery charger to charge them in parallel.. Lifepo can be at the same voltage but different states of charge.

 

[Solar Bear]

So my old 12V 6 amp is OK to use on the Lifepo? I wasn't sure if that could be used. Thanks.

 

[wholybee]

Whatever charger you use, they need to be charged to about 14.2v or higher, and the same voltage. Then make sure they stay the same voltage once disconnected for a while.

 

[Solar Bear]

Great. Thank you.

 

[GSXR1000]

So my old 12V 6 amp is OK to use on the Lifepo? I wasn't sure if that could be used. Thanks.

sure.. I used a harbor freight battery charger when I charged my build between test. it just won't restart charging some lifepo voltage doesn't drop during use but that doesn't matter. they charge to about 14.2v I believe
Also you have a BMS as a fail safe

 

[JulianG]

Make sure the BMS in each battery can be connected in series many do not.

 

[Solar Bear]

Thanks.