Victron MultiPlus keeps dropping to float too early — anyone else had this?

Had exactly this with my MultiPlus-II in the motorhome last summer. Kept floating after maybe 20 mins of absorption even though the Fogstar lithium pack was nowhere near full.

Turned out my absorption voltage was set slightly too high — the BMS was seeing it as "close enough" and signalling done early. Dropped it by 0.2V and the behaviour settled right down.

Few things worth checking:

• Are you running with a BMS that talks to the MultiPlus via DVCC? If so, the BMS is essentially in charge of charge termination, not your MultiPlus settings
• What's your tail current set to? On lithium especially, if it's too high a percentage it'll cut to float before the battery's properly topped
• Firmware up to date? There were some quirky charging profile bugs in older versions

Also worth looking at whether it's temperature related — my setup in the shepherd's hut does odd things in cold weather because the battery temp sensor reads low and the unit gets conservative.

Stick your battery type and BMS make in if you can, and whether you're on VE.Bus Smart Dongle or full Cerbo setup — makes it easier to pinpoint. Quite a few variables at play here.

Anyone else seen this on a straight AGM setup rather than lithium? Curious whether it's as common.

@ST_Builds classic symptom of the tail current threshold being set too aggressively for lithium. The MultiPlus defaults assume lead-acid behaviour — it's watching for current to taper as a sign of full charge, but a healthy lithium pack can hit that threshold whilst still genuinely accepting charge.

In VE.Configure, check your "Absorption current threshold" — I had mine accidentally left at 4% of bank capacity. Dropped it to 1–2% and the absorption phase extended properly.

Also worth verifying your battery capacity setting is accurate. If the MultiPlus thinks you have a smaller bank than you do, the maths goes wrong immediately.

My 280Ah Fogstar cells needed the threshold down at around 3–4A before float was appropriate. Every lithium pack behaves slightly differently so log it overnight with VRM and watch the actual tail current curve before deciding.

Great thread, this caught me out too last season! Worth checking your repeated absorption setting in VEConfigure as well — if it's disabled or set to a long interval, the charger won't re-trigger absorption even when the battery genuinely needs it after a partial cycle.

Also @ST_Builds, are you running a BMV or SmartShunt alongside? Enabling DVCC through Venus OS and letting the BMS communicate actual state of charge made a massive difference on my setup. The MultiPlus stops guessing based on voltage alone and actually responds to what the battery is telling it.

@RetiredSquaddie is spot on about the tail current — Fogstar themselves recommend around 2-4% of capacity as the cutoff figure in their documentation, so worth cross-referencing that against whatever's currently configured.

Really useful thread — I'm in the middle of setting up a Victron MultiPlus-II for my garden office build and this is exactly the kind of thing I'd have stumbled into.

Quick question for the group: does the tail current threshold need adjusting differently depending on battery capacity? I've got a Fogstar Drift 200Ah and I'm wondering what percentage people are actually running for lithium in a relatively static (non-vehicle) application.

Also, is VEConfigure the only way to change this, or can it be done through VictronConnect on a phone? I don't have a laptop with a VE.Bus cable yet and I'm trying to avoid buying one if possible.

@IvyDai — did the repeated absorption setting need changing too, or was the tail current fix enough on its own?

@ST_Builds had almost identical on my narrowboat last winter — MultiPlus-II 12/3000 paired with a 200Ah Fogstar Drift. The thing that finally sorted it wasn't just the tail current threshold but the absorption voltage being fractionally low, causing the BMS to report near-full prematurely via the VE.Bus BMS comms.

Worth checking in VEConfigure3 under the Charger tab — if you're running proper VE.Bus BMS integration, the "BMS controls charger" flag can override your absorption timer entirely, handing authority to the BMS. Once I understood that handoff was happening, the logic made sense. The BMS was correctly terminating absorption; my absorption voltage was just set 0.1V too low so it was hitting that point far too quickly.

@TransitConvert — worth factoring this into your garden office design before commissioning rather than after.