2 x 12v Lifepo4 in Parallel.

[tz1280]

I just bought 2 x cheap ($290 US) generic supposedly prismatic 12v 135ah slim form batteries from a fairly reputable seller that I intend to use in parallel. i understand they need be the same voltage before linking them. I’ve been charging them with a Victron IP67 25 amp charger with the llifepo4 preset.

I finding that one battery is consistently around .1 of a volt lower ( 13.5 vs 13.6) that the other after leaving them for about 12 hours each on the charger.

Can I discharge the higher voltage battery slightly to bring it to the same voltage as the other and then connect them in parallel?

 

[DThames]

Yes. That is what I do.

You could (instead) put a current limiting resistor between them so no huge rush of current, then remove the resister after they were the same. Sorts itself out that way.

 

[DThames]

Here is another way to do it. Get some of these little test leads. Use one of them to complete the parallel circuit. The wire is tiny and will act both like a resistor and a fuse. If the lead don't get hot, leave it until zero amps, then the batteries are the same voltage. If the batteries are fully charged or near discharged, 0.1v will not cause much current anyway. Just connecting them with a tiny wire is a way to do it and not allow huge amps (the wire would smoke if amps were very many).

 

[notarichman]

i have the same problem and want to know if you can use a 4s balancer to balance the two batteries.

 

[DThames]

2P balancer

Resistor

 

[GLC]

I just bought 2 x cheap ($290 US) generic supposedly prismatic 12v 135ah slim form batteries from a fairly reputable seller that I intend to use in parallel. i understand they need be the same voltage before linking them. I’ve been charging them with a Victron IP67 25 amp charger with the llifepo4 preset.

I finding that one battery is consistently around .1 of a volt lower ( 13.5 vs 13.6) that the other after leaving them for about 12 hours each on the charger.

Can I discharge the higher voltage battery slightly to bring it to the same voltage as the other and then connect them in parallel?

A .1 or .2 volt difference is not going to effect anything.

 

[tz1280]

Thank you DThames for the assistance and GLC for the assurance.

I have since had the laggard battery on the Victron‘s absorption charge at 10A for another 12 hours putting in 2.4 amps in that time. After resting it for 8 hours the voltage differential is now apparently just a.02 of a volt.