Anyone else running lithium in a van AND a boat — different BMS behaviour confusing you?

Got a bit of an odd one. Running Fogstar Drift 100Ah in the van conversion and a Victron Smart Lithium 100Ah on the boat. Both 12V, both charged via Victron kit, but the BMS behaviour is noticeably different — especially around low-temp cutoff and cell balancing timing.

The Fogstar on the van trips its low-temp protection somewhere around 5°C which is a pain in the neck when I'm parked up in winter. The Victron on the boat seems far more forgiving in practice, though obviously the two aren't directly comparable given the price difference is significant.

Wondering if anyone's run both and actually done a side-by-side on BMS cutoff thresholds? I've got a SmartShunt on each setup and the data is interesting but I'm not sure I'm reading it right across two different systems.

Is there a way to configure the Fogstar low-temp cutoff, or is it fixed in firmware? Can't find a straight answer anywhere in the docs.

DerekYoung76 | Posts: 847 | Location: Scottish Borders

@GoldenGaffer Ha, I'm in almost the exact same situation — Fogstar Drift in the van, Smart Lithium on the narrowboat. The thing that caught me out early on is that the Fogstar's BMS is far more "passive" in how it communicates. It'll just quietly disconnect without any warning to your Victron kit, whereas the Smart Lithium talks directly to the DVCC system and gives the whole setup a proper heads-up before anything dramatic happens.

Worth making sure your van setup has a BMV-712 or similar so you're at least seeing what the Fogstar is doing, since it won't shout about it otherwise. The boat essentially manages itself once VE.Bus is configured properly.

What Victron chargers are you running on each? That might help narrow down what's confusing you.

WelshCamper | Posts: 1,203 | Location: Wales

Running almost identical configs here — Fogstar Drift in the van, Victron Smart Lithium on the boat.

The key thing that caught me out: the Fogstar's BMS is far more aggressive on high-voltage cutoff than the Victron's. I had my MPPT set identically on both initially — 14.6V absorption — and the Fogstar would occasionally trip out mid-charge whilst the Victron sailed through without complaint.

Worth checking your cell-level balancing thresholds too. The Victron Smart Lithium communicates directly via VE.Bus/BT and can tell the MPPT to back off gracefully. The Fogstar has no such integration, so it's essentially a hard disconnect when limits are hit.

My fix on the van was dropping absorption to 14.4V and reducing tail current sensitivity. Zero trips since.

What symptoms are you actually seeing — unexpected shutdowns, or something else @GoldenGaffer?

Gazza89 | Posts: 412 | Location: Yorkshire

Interesting thread this! One thing worth flagging that I don't think's been mentioned yet — the Victron Smart Lithium has that VE.Bus BMS integration which actively communicates with other Victron kit to signal charge/load disconnect. The Fogstar Drift's BMS is much more self-contained and just cuts passively at voltage limits without that kind of chatter.

So if you're seeing differences in how your MPPT or DC-DC charger responds to a BMS event, that's likely why. The Victron ecosystem is almost expecting to have a conversation with the battery, whereas the Fogstar just quietly handles things itself.

Not better or worse necessarily, just fundamentally different approaches. Might be worth checking your DVCC settings in Victron Connect if you're running a Cerbo — could explain some of the behaviour you're seeing @GoldenGaffer.

LesWood78 | Posts: 2,156 | Location: Array

Worth clarifying something nobody's mentioned yet — the Fogstar Drift uses a built-in BMS with fixed protection thresholds whereas the Victron Smart Lithium is essentially a "dumb" cell pack that relies entirely on the external Victron BMS or DVCC ecosystem to function safely.

That's why behaviour feels so different. The Fogstar will just disconnect under fault conditions, full stop. The Victron Smart Lithium communicates via VE.Bus/BMS12/200 and can request charge current reductions rather than hard-cutting.

I've got a similar mismatch between my shepherd's hut setup and a van build — different BMS architectures even with identical Victron chargers at both ends caused endless confusion until I properly read the Victron BMS12 integration docs.

Key question @GoldenGaffer — are you using the Cerbo GX or similar on the boat? That changes everything about how the Victron battery communicates.

LesHarris | Posts: 412 | Location: Somerset

@GoldenGaffer The key thing worth understanding is that the Victron Smart Lithium has its own integrated BMS communicating directly via VE.Direct or VE.Bus with your Victron chargers — so the whole system talks to itself and reacts accordingly. The Fogstar Drift uses an internal BMS but it's essentially silent in that ecosystem; it protects itself but doesn't communicate upstream to your charger.

What this means practically is the Victron battery will actively instruct your charger to back off, whereas the Drift just disconnects if things get out of hand. Different philosophies entirely, which is probably what's catching you out.

Are you using a SmartShunt or Cerbo on either setup? That might help clarify what's actually happening at the BMS level on both systems.

PaulMurray | Posts: 47 | Location: Array

Running a similar setup in my tiny house on wheels — Fogstar Drift as main house bank. One thing that caught me out early on: the Fogstar's BMS will disconnect hard under certain fault conditions with zero warning to your charger, whereas the Victron Smart Lithium is designed to "talk" to other Victron kit via the VE.Bus/BMS comms cable and give a managed shutdown instead.

So if you're seeing your Victron MPPT throwing errors only on the van side, that's probably why — it's not expecting a sudden disappearing load/source.

Have you got the Victron BMS 12/200 or a Battery Protect inline on the van setup? That helped me manage the communication gap between non-Victron lithium and Victron charge sources considerably. Made behaviour much more predictable.

Not my exact setup — I've got Fogstar Drift in my shepherd's hut rather than a van — but same BMS behaviour questions cropped up for me.

One thing worth adding: the ambient temperature matters more than people realise with these two units. The Victron Smart Lithium is noticeably more conservative about cold-weather charging cutoffs via the BMS versus the Fogstar. If your boat's sitting in a marina through winter, that difference will catch you out.

Check your VictronConnect BMS Assistant settings carefully. They're not identical defaults between the two systems, which explains a lot of the "odd" behaviour you're seeing.

Something I noticed running between my motorhome and the narrowboat is that ambient temperature plays a huge role in how differently the two BMS units behave — especially on cold mornings.

The Victron Smart Lithium will actually cut low-temperature charging protection far more conservatively than the Fogstar Drift, which caught me out one February mooring near Devizes. Woke up expecting full batteries and got a confused Multiplus instead.

@GoldenGaffer — worth checking your Victron app for any low-temp events logged overnight. The Drift is more permissive below 5°C, so if you're comparing behaviour across the two setups, that temperature threshold difference could explain a lot of what you're seeing.