SOC difference before parallel connection

[Ligando]

Okay. I looked through the forums a bit before posting this and haven’t found my answers yet.

This is a parallel system setup of 2x 200Ah Renogy LiFePO4 Smart Batteries.*

1) The battery showing the cell under voltage warning:

Is it really bad that it’s like this? I’m not even sure what happened. While installing a secondary alternator kit, I had my power bank partially disconnected (all breakers off but can’t remember which 4/0 cables were disconnected when reconfiguring). I definitely didn’t plug anything back in incorrectly and run things, all loads were disconnected the whole time. But I think I disconnected the battery with the issue, partially or wholly, while the other stayed connected to the bus bars.

Currently recharging this with a Battery Tender Junior 800 for LiFePO4 and it’s taking forever to top off.

2) Is this too big a difference to reconnected the whole system (again, in parallel)? I understand that it may not be ideal to do so, but would it be possible that they batteries could balance together when reconnected to the system and getting charged by the alternator?

I’m running out of time to get this done today and get on the road early in the morning.

Any help/insight would be greatly appreciated!!!

 

[RCinFLA]

I think their software writers needs instructions on displaying significant digits.

Battery Tender junior at 800 mA. 400 AH's to charge. Only 500 hours to get there.

 

[time2roll]

Unless you can run the existing battery down within 500 mV of this second battery (13.0 volts) I would not just connect them in parallel.
Getting the voltages closer and charging with the system will be faster than the BTJ-800.

 

[Ligando]

I think their software writers needs instructions on displaying significant digits.

Battery Tender junior at 800 mA. 400 AH's to charge. Only 500 hours to get there.

Should’ve looked at that… it’s the only charger I have besides the secondary alternator, 450W panel, and inverter charger. None of which can I connect to until I’m certain it’s safe. Also, I’m only working on charging the battery with the low voltage warning, so that’s one 200Ah battery, not the whole bank (2x 200Ah).

I just need to know if it’s safe to hook it all up and let the BMS balance everything out with the alternator/solar providing more charge than this damn little charger (got it for the motorcycles).

 

[Ligando]

Unless you can run the existing battery down within 500 mV of this second battery (13.0 volts) I would not just connect them in parallel.
Getting the voltages closer and charging with the system will be faster than the BTJ-800.

Thank you, that’s helpful! I’m going to hook up the one that’s low to the rest of the system, run the engine to charge it, get it to 100% that way.

 

[RCinFLA]

I just need to know if it’s safe to hook it all up and let the BMS balance everything out with the alternator/solar providing more charge than this damn little charger (got it for the motorcycles).

You will not get much, if any, balancing by BMS until it gets close to full charge. A cell needs to be greater than 3.4v to get balance bled.

 

[Ligando]

So, I’m seeing the SOC as 100% but voltage is 12.4. I have it hooked up to the inverter charger and plugged into shore power. Cells 1-4 show 3v, 3v, 3.4v, and 2.9v, respectively.

What’s gives? Do I keep it on charge until it balances?

 

[Ligando]

Welp… connected to shore power for less than 20 minutes and everything is back to normal.

Thanks everyone for your responses and insight!