Swapped to lithium on my narrowboat – shore power charger now playing up

Done the same swap on my motorhome and the charger drama is basically a rite of passage at this point. 🎉

The issue is almost certainly your charger still running a lead-acid profile — it'll be pushing absorption voltages that are too high and probably not cutting off cleanly at the top, which makes lithium BMS's rather grumpy.

A few things worth checking:

• Does your charger have a lithium/LiFePO4 mode? Some older units have it buried in a settings menu nobody's ever opened
• What's the bulk/absorption voltage set to? For LiFePO4 you want around 14.2–14.6V for a 12V bank, not the 14.8V+ some lead chargers default to
• Is the BMS cutting out mid-charge? That's usually the charger not recognising the flat absorption curve and going into a weird fault state

On my motorhome I ended up chucking the old charger and going with a Victron Blue Smart — pricey but it actually speaks LiFePO4 properly and the Bluetooth monitoring is genuinely useful when you're trying to diagnose what went wrong at 11pm on a mooring.

Fogstar cells? Fogstar Drift batteries have caught on a lot lately on the narrowboat scene from what I've seen — curious what brand you went with and whether it came with any BMS documentation that specifies the charging parameters.

What charger are you currently running? Might help narrow it down — some are fixable with a profile change, others are basically just marine-grade paperweights at this point.

@Smithy nailed the diagnosis — worth adding that some older chargers (particularly anything pre-2018 Victron Blue Smart era) will also run an equalisation cycle that can spike voltage dangerously high for lithium cells. On my Vivaro build I had a Sterling Pro Charge Ultra doing exactly this — a perfectly capable unit, just needs its DIP switches reconfigured for lithium. Check your charger's manual for a dedicated lithium programme or at minimum a "gel" profile (typically 14.2–14.4V absorption, no equalisation). If your BMS has a high-voltage cutoff around 14.6V you'll likely see it tripping repeatedly until the profile is corrected. The Victron Blue Smart IP22 is popular on narrowboats for good reason — proper lithium presets out of the box and Bluetooth monitoring.

Went through exactly this on my shepherd's hut setup last year. Even when you can set a lithium profile, double-check what voltage the charger actually outputs at — mine claimed "lithium compatible" but was still floating at 13.5v which is basically useless for Fogstar cells.

Worth grabbing a cheap multimeter and just measuring at the battery terminals while it's charging. Numbers don't lie.

Also check your battery BMS specs — some want absorption voltage bang on 14.2v, others are happy up to 14.6v. Getting that mismatch wrong either undercharges or stresses the pack.

Great thread this — narrowboats have the added complication of shore power quality varying massively between marinas, which can throw another spanner in the works on top of the profile issue.

One thing worth mentioning that nobody's touched on yet: if you're running a BMS with low-temperature cutoff (and you should be on a boat sitting in cold water), make sure your charger handles the sudden disconnection gracefully. Some cheaper units throw fault codes or lock out entirely when the BMS cuts the circuit, and then you're scratching your head wondering why it won't restart without a manual reset.

Also worth checking what your marina's shore power pedestal is actually delivering — I've seen some older ones drooping well below 230V under load, which causes all sorts of odd charger behaviour that looks like a settings problem but isn't. A simple plug-in voltage monitor will tell you quickly.

Good shout from @PaddyFox on shore power quality — that's a real narrowboat-specific headache. Worth picking up a simple plug-in power monitor (Brennenstuhl do decent ones for under a tenner) to check what voltage and frequency you're actually getting at the hookup point. Some older marina pedestals are genuinely shocking — no pun intended! I've seen 210V coming through on a "240V" hook-up, which can cause chargers to behave erratically regardless of your battery profile settings. If the voltage is consistently low, your charger may never reach the absorption stage properly, which'll look like a faulty lithium profile but is actually a supply issue upstream. Sort the incoming power quality first, then look at your charger settings — saves a lot of head-scratching.