Battery Question; I have 2 LiFePo batteries but different brands: can I use them together?

[tinspoons]

Hello, first time post and have some basic battery questions I can't seem to find answers for from a general search. I had2 100w panels on the van with 1 100ah 12v LiFePo SOK battery. Then I decided to get another battery but SOK was sold out of the same battery so I bought a LiFePo battery from Renogy and hooked them up in parallel (keeps the voltage the same at 12v).

Is this okay? I saw the Renogy manual said that you shouldn't mix battery brands even if its the same chemistry, is this right?

Also, what's an easy way of finding out if both batteries are charging? Do they both charge together or one first and then the other? The Renogy charge controller (20A MPPT) says the battery is at 100% but it said that when I had just the one charging. Is it smart enough to figure out I added another battery? Any easy way to make sure everything is wired correctly and that both are being used?

I did get a battery monitor wired up but I figured I'd just let everything charge completely to calibrate it rather than drain them completely.

Thanking you in advance for any good advice and answers the community provides!

 

[Steve_S]

In Series that can create serious issues and not intended for complete Lithium Based Battery Packs.
In Parallel there really is no problem is correctly wired. BUT Different AH Capacities can lead to issues, especially if far apart.

The GOTCHA is key. When commissioning batteries in parallel they must be at the same voltage/soc or one will try to back charge and that's not good. Once both are equal charge & connected then you do have to add the added AH & kWh etc to the software so it knows battery bank size.

20A to charge 200AH is pretty short BTW. 100AH battery pack can take 50A charge to 85-90% and then Constant Voltage Variable current (float) to finish to 100%. 100% meaning 3.500Vpc or 14.0V.

ALSO - There is NO POINT in charging over 3.500Vpc (14.0V) as that is the cliff climb to 3.650 Volts per cell. Working Voltage Range for LFP is 3.000-3.400 with nominal voltage being 3.200 per cell. 4 Cells for 12V battery.
Bulk Charge to 14.0V
Float at 13.8V
Reset to Bulk @ 13.6V
EndAmps/TailCurrent is 10A for you battery packs.

Download this resource PDF, pages 12 & 13 have an extended voltage charge and matrix that will answer many questions.
Luyuan Tech Basic Lifepo4 Assembly Guide

Hope that helps, Good Luck.
Steve

 

[tinspoons]

Thanks for the reply. Maybe I seemed more knowledgeable than I am, but I'm not sure you answered my questions. Apologies if you did but I just didn't understand it. I'll bullet my questions directly and maybe you or some other kind soul will give me an answer.

Can I use 2 different battery brands of the same chemistry LiFePo4 and amp hours 100 without any issues?
I have both batteries wired in parallel: is there a way to know they're both charging?

I had one battery (SOK) and then I added another (Renogy) so I'm not sure how to know that they're both charged by the solar panels (2 100w).

 

[Steve_S]

Both if Identical Chemistry & AH Capacity will live fine together. When in Parallel you will see charging going on. Without a smart BMS with access to the internals it's not possible to see what's up inside. You could put a Shunt between each pack & the common DC BusBar, OR a Hall Pickup type (no cutting wires) which can monitor in/out electrons and even give AH/AH numbers as well.