Help with balancing 12V lithium batteries in series

Q&A and troubleshooting
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Dear community members,

I currently have a Victron Energy 24V system installed in my motorhome, paired with two Renogy 12V 200Ah lithium batteries connected in series (12V + 12V = 24V).

I’m running into an issue where the batteries don’t stay balanced. Every 40–60 days I need to charge them individually, and the system often cuts off at around 80% capacity.

My solar setup consists of two 450W panels wired in series.

Current system components:

  1. 2 × 450W solar panels (in series)
  2. Victron MPPT 100/50
  3. Isolated 24V → 12V DC/DC converter (30A)
  4. Battery monitor
  5. 24V 3000W inverter

I’m looking for a reliable solution to keep the batteries properly balanced so that one doesn’t sit at 14.10V while the other is at 13.20V.
Ideally, I want both batteries to reach full charge at the same voltage without needing to separate and charge them manually.

Any advice or recommended setup changes would be greatly appreciated.

Thank you!

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Try one of these: Battery Balancer | Victron Energy

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Thanks for sharing, Is this working for LifepO4 batteries?

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Your main issue is likely what @bachete said but also are the Renogy batteries “Smart” batteries? There have been numerous issues like you describe experienced by users with these drop in style “smart” batteries not charging or discharging evenly.

If this is the issue no amount of changing the way it is wired or tightening terminals will help.

1 Like
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@bachete This is the second time I have seen you confuse series and parallel in answering this tupe of question. It is a bit of basic electrical fundamental to get wrong when putting yourself as being knowledgeable. If the batteries are in series then you must by definition have the same current flow through both batteries because there is only one path for the current. If one connection is loose then you just have a high resistance joint loosing voltage BUT the same current still flows through both batteries. What you are describing refers to parallel connection. Are you just copying what you have read from AI rather than actual knowledge.

In series differences occur due to poorly matched cells in cheap batteries with different capacities, leakage currents, different internal resistances, BMSs that have differentparasitic loads from the cells and low current balance boards thatdo not rebalance the cells quickly enough. It is always better to have a single 24V battery than 2 12V batteries in series.

3 Likes
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Yes

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Hi everyone, can anyone tell me if the wiring is correct?

Don’t laugh at the setup — some kind of ‘authorized’ electrician did this, haha.

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Electricians need to stick to installing wiring that gets covered by walls.

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@lmario As far as I can tell ftom that dim photo it looks mostly correct for a 24V system. One thing worries me though, on the battery that is at the bottom of the photo you have one or two 12V wires going somewhere. What are these wire connected to, is it to a 12V load. This could be the cause of your imbalance, you MUST NOT take a 12V load off a 24V set up like this because it will imbalance your batteries. You must use a 24V to 12V DC to DC converter such as a Victron Orion.

1 Like