Victron 200Ah lithium showing 14.4v but BMS keeps cutting out at 80% — anyone seen this?

Had almost exactly this with my Fogstar Drift 200Ah last winter up at the cabin. Drove me absolutely mad for about three weeks before I tracked it down.

The 14.4v you're seeing is your Victron charger doing its job correctly — that's not the villain here. The BMS cutting at 80% is almost certainly a cell imbalance issue rather than an overall voltage problem. What's happening is one cell group is racing ahead of the others and tripping the BMS overvoltage protection before the pack as a whole reaches full charge.

A few things worth checking:

• Individual cell voltages — you'll need a proper BMS app or a decent multimeter across each group. I use the Fogstar app but others swear by the JK BMS for visibility
• Absorption time — if your Victron is hitting 14.4v and then immediately floating, the weaker cells never get chance to catch up. Try extending absorption to 2–3 hours
• Temperature — my BMS got extremely twitchy below about 5°C. Are you storing yours somewhere cold?

The 80% cutoff being so consistent suggests it's the same cell group every time, which is actually reassuring in a strange way — random cutoffs are worse.

Worth pulling the Victron MPPT or MultiPlus logs too if you haven't already. The history screen tells a proper story once you know how to read it.

What BMS is actually inside yours — is it the stock unit or have you swapped it out? That'll change the advice considerably. Others on here will have more specific knowledge depending on the brand.

@MountainBarry really interesting that you saw this with the Fogstar too — makes me wonder if it's more of a systemic issue than something specific to Victron's own batteries.

Few questions before I chip in with anything useful:

• What's your charge current set to on the MPPT/charger?
• Are you seeing the BMS cutout happen during bulk, absorption, or float?
• Any temperature sensors fitted to the battery itself?

I had a vaguely similar thing with my setup where the cell imbalance was triggering the BMS rather than actual overvoltage — the pack looked fine at 14.4v overall but one cell was spiking ahead of the others internally.

Have you got access to the individual cell voltages? If you're using a Victron system you might be able to pull that data through VictronConnect if the BMS supports it. Could save you weeks of head-scratching like @MountainBarry experienced.

Great thread this. @MountainBarry curious whether yours turned out to be cell imbalance triggering the BMS, because that's my first suspicion here. 14.4v at the pack level can look perfectly healthy whilst one rogue cell is quietly racing ahead and hitting its high voltage cutoff before the others have caught up. The BMS then pulls the plug and from the outside it just looks like a random dropout at 80%.

Worth grabbing a Bluetooth BMS app if yours supports it and watching individual cell voltages during a charge cycle. You're looking for any single cell diverging more than about 50-80mV from the rest as you approach that 80% mark. If that's what you find, a proper top balance might sort it, though if the cells have drifted significantly it can take a few cycles to settle down.

What charger profile are you running?

@MountainBarry @Wayne1996 — did either of you check the BMS logs before the cutout? I'm having something similar with my setup and wondering whether the over-voltage protection threshold on the BMS itself is set lower than what the Victron is pushing out.

Specifically — is 14.4v actually too high for a 4S LiFePO4 pack? That works out at 3.6v per cell which is right at the top of the safe window. If one cell is already slightly high before charging begins, could the BMS be seeing 3.65v+ on that cell even while overall voltage looks fine on the Victron display?

Has anyone used a proper cell-level monitor to check individual cell voltages during the charge cycle rather than just relying on the pack voltage reading?

@AlanPalmer57 the BMS logs are worth pulling if you can get them, but in my experience with emergency backup setups the culprit is often the charge current setting on the Victron being too aggressive for what the BMS is rated to accept at that SOC threshold.

Worth checking your absorption voltage is actually set to what the battery manufacturer specifies — Fogstar and others are quite specific about this. If the Victron is pushing 14.4v hard while the BMS is seeing one cell edge toward its upper limit, it'll trip before the overall pack hits 100%.

What's your charge current set to relative to the battery's max continuous charge rating? Even being 10-15A over can cause intermittent BMS trips that look completely random until you correlate the logs with the charge curve.

@MountainBarry what was the actual fix in the end? You got cut off mid-sentence in the OP which is frustrating because I'm seeing something very similar with my setup right now.

Mine is a Renogy 200Ah with their own BMS — cutting at roughly 80% SoC, voltage looks fine on the Victron MPPT side. I'm wondering whether it could be a temperature-related cutoff rather than cell imbalance? It's been cold here and the battery is in an uninsulated compartment. Some BMS units have a low-temp charge protection threshold that kicks in surprisingly early.

@Spud74 agreed the logs would be useful — does anyone know if you can pull detailed BMS logs from the Renogy batteries, or are they more of a black box compared to something like a Victron Smart Lithium?