2 x 12v 100ah LiFePo4 renogy smart batteries in parallel only pulling power from one battery

[ahorvath13]

Hi, I am brand new to solar and battery back-ups and recently installed a Renogy 200w off grid solar kit to the roof of my sprinter van as part of my conversion to a camper. Everything seemed fine when I first set everything up (batteries displaying similar SOC % and voltages, and amperage draw while in use). Recently through on my Renogy DC Home app I've been seeing one battery charge to usually 14.2 volts and discharge fine. However, the other battery seems to only charge to 13.6 or 13.7 and appears to have no draw coming from it (maintains 100% SOC and voltage) when using 12v power, but the other battery drains. If I add a large load to my inverter (like a heat gun) the "sleepy" battery seems to "wake up" and I start to see an even amperage draw from both batteries.

I'm stumped and any help is greatly appreciated

 

[Tomthumb62]

I see nearly this exact post on this forum about once a week. Maybe it’s more and I didn’t see it.

If I were you, I’d return those Renogy batteries if you still can. They’re overly complicated and the end result is problems like this. They should work just fine out of the box and never give you problems, but these Renogy batteries aren’t well designed or built or maybe both.

If you try Renogy customer support, don’t waste your time doing it over email. It could take weeks or months. Call. You might not get results until you ask or they offer to push your case up the chain. Tier 2 has some clue and Tier 3 is quite good. But good luck getting to those tiers!

Let’s assume though that the problem is your wiring and not the batteries. I doubt it’s the wiring, but let’s check it out anyways. Got a schematic and photos of your wiring and system?

 

[Alkaline]

$50.00 bet says you have unequal length wires, where 1 battery wire(s) is shorter is closer to the inverter than the other one and that is the one that is charger/discharging while the other just sits and yawns.

I bet if you swap the battery positions than magically the other battery is what will be charging better discharging more.

I'll tell you the fix but first I want you to try the above.

 

[ahorvath13]

I see nearly this exact post on this forum about once a week. Maybe it’s more and I didn’t see it.

If I were you, I’d return those Renogy batteries if you still can. They’re overly complicated and the end result is problems like this. They should work just fine out of the box and never give you problems, but these Renogy batteries aren’t well designed or built or maybe both.

If you try Renogy customer support, don’t waste your time doing it over email. It could take weeks or months. Call. You might not get results until you ask or they offer to push your case up the chain. Tier 2 has some clue and Tier 3 is quite good. But good luck getting to those tiers!

Let’s assume though that the problem is your wiring and not the batteries. I doubt it’s the wiring, but let’s check it out anyways. Got a schematic and photos of your wiring and system?

I'll have to get in touch with renogy asap to see what they say about returning just the batteries since they came with the full kit, fingers crossed. I wish I would have read more forums on renogys batteries before I purchased.

I attached a very rough hand drawn schematic of my wiring. Everything is currently roughed in with all of the wires at the length they arrived at with the excess coiled up

 

[ahorvath13]

$50.00 bet says you have unequal length wires, where 1 battery wire(s) is shorter is closer to the inverter than the other one and that is the one that is charger/discharging while the other just sits and yawns.

I bet if you swap the battery positions than magically the other battery is what will be charging better discharging more.

I'll tell you the fix but first I want you to try the above.

I'll try and swap battery positions the next chance I have (weather permitting). Currently my set up is roughed in with all of the wires the length they came in the kit and the excess coiled up. The only extra I've added is a 2 foot length between the shunt and the negative terminal of my paralleled batteries. Is that extra 2 foot something that could cause problems?

 

[TacomaJoe]

I would move the vehicle frame ground from the negative battery terminal over to the other side of the shunt (same place as all other negatives).

 

[ahorvath13]

So here's were I'm at now with my system. My shunt and body ground were the last additions to my system and it "seemed" to function as it should before they were added. So I remover them both to have all equal length wires and at the same time swapped the position of the batteries. After doing so I connected everything again, without the shunt and body ground, and I still have the same problem with the same battery after a sunny day.

Today (the day after the previous steps were done) I pulled both batteries out. According to my Renogy DC Home app both batteries were at 100% SOC when pulled with the charge controller contributing no additional charge to them via PV. Once disconnected I checked the voltages at the terminals of each with a multi-meter and the app. Battery 1 (the good one?) stated on the app that it had a charge of 14.1V and my Multi-meter showed 14.11V. Battery 2 (the not so good one?) stated on the app that it had a charge of 13.6V but my Multi-meter shower me 13.28V. Do either sound like a battery that is no good? I've read that it should rest at 13.6V, is that correct?

 

[TacomaJoe]

Sure looks like a bad battery to me. Swapping positions didn't make a difference on charging. Battery 2 has a problem (weak cell?).

 

[ahorvath13]

Thank you all for your help, I am currently working with renogy to return my batteries. I think a simpler single 200ah battery setup may be in my future

 

[Tomthumb62]

I think a simpler single 200ah battery setup may be in my future

Top of the list of Will Prowse’s recommended budget LFP 12v batteries is the Powerurus. His tear down video convinced me to try it. Loving it so far and customer service has been excellent in answering all my technical questions. They have 200Ah and 100Ah models. The 200Ah has a 200A BMS. All models have low temp protection and Bluetooth/app. Made by Roypow, who has an excellent reputation.

LiFePO4 Batteries for Offgrid and Mobile Solar

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Edit: until recently, the Powerurus was at the top of Will’s list, but it seems he puts Litime at the top now, likely due to the lower list price. However, the Powerurus is on a long term sale. I paid $730 shipped for the 200Ah. No tax and if your email them, they’ll send you a coupon for an additional $20 off. $750-20=$730.

 

[mikefitz]

You are charging the batteries with a poor quality PWM controller with fixed charge voltages. Since some Renogy batteries often have poorly balanced cells, the BMS will shut down the battery due to cell over volts that occurs at high charge volts. This is perhaps what you are seeing with the problem battery.
If you hold the problem battery at a lower charge voltage, say 13.8 volts, for several hours, the balance should improve.
If you post a screen shot of the cell volts in the problem battery, ( when it's in a shutdown state) , this would help the discussion.

Mike

 

[Aussieguy]

vehicle body ground.............................. hook it to the front of the shunt with all the rest of the neg cables?

use a decent negative busbar if needed.
Busbar and shunt connected to the battery that does not have the main positive feed.