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

Done this exact swap last spring on my 57ft trad. Absolute game changer but yeah, the shore power side caught me out too.

Old charger was a basic 3-stage unit that technically worked with lithium but was throwing the BMS into protection every other day. Turns out it was holding a float voltage that the Fogstar cells absolutely hated long-term.

Chucked it and went full Victron — Blue Smart IP22 shore side, paired with a Quattro for the inverter duties. Bit of an outlay but the DVCC settings in VictronConnect let you dial everything in properly. BMS and charger actually talk to each other now rather than fighting like a pair of blokes in a pub car park.

Few things worth checking before you spend owt:

• What's your BMS? Some cheaper units have rubbish absorption cutoff comms
• Is the charger genuinely lithium-compatible or just marketing fluff? Big difference
• Check your charge current limits — lithium can accept high current but your wiring might not fancy it

What charger are you running currently? And which cells — DIY pack or something like a Fogstar Drift? Makes a difference to the advice really.

Also — marina shore power quality is often minging. Had a voltage drop at Braunston last summer that was confusing my kit something rotten. Worth chucking a cheap voltage monitor on the hookup just to rule that out.

Plenty of folk on here have sorted similar. What's it actually doing when it plays up — tripping, refusing to charge, or just weird readings?

@GrumpySparky the absorption voltage ceiling is the killer with those old units — most are capped at 14.4V which sounds fine on paper but they'll sit there for hours trying to "top off" because the current never drops enough to trigger the termination logic. Lithium accepts charge so efficiently that the charger just gets confused.

On my static caravan I had the same issue with a legacy unit before I swapped to a Victron Blue Smart IP22. The lithium preset sorts it properly — absorption timeout kicks in correctly rather than relying purely on tail current.

Worth checking whether your existing unit has a lithium profile buried in the settings before binning it entirely. Some mid-range Ctek and Sterling units do, just poorly documented. What make/model is the problematic charger?

@MandyRoss yeah the voltage ceiling thing is well documented but honestly the bigger issue people miss is the absorption timer — old units just sit there pumping current at that stage for ages even if the battery's already full. Lithium doesn't want that.

Swapped out my old Sterling unit on the static for a Victron Blue Smart IP22 and haven't looked back. Set a proper lithium profile, job done.

On the narrowboat specifically — worth checking if your BMS has a high voltage cutoff because that's your last line of defence if the charger misbehaves. Some cheap units don't communicate with anything, they'll just keep going until the BMS trips and then you're cycling the BMS constantly which isn't ideal.

What charger are you actually running now?

Hey all, great thread. Just to add something nobody's mentioned yet — even if you sort the voltage settings, a lot of older shore power chargers have a temperature compensation circuit that's tuned for lead-acid. It'll automatically drop the charge voltage in warmer weather, which is the opposite of what you want with lithium (they don't really need temp compensation at all). On a narrowboat sitting in the sun all summer, that circuit could be quietly undercharging your bank without you ever realising. Worth checking if your charger has a dedicated "lithium" mode that disables temp comp entirely, or whether you need to think about replacing it. Victron's IP22 or IP65 range are popular choices for shore power on boats and handle lithium properly out of the box. @GrumpySparky what charger are you currently running?

@Cleggy83 raises the thing nobody wants to hear — your shiny new Fogstar cells deserve a charger that actually knows lithium is a thing that exists, and my old 3-stage unit treated them like confused AGMs having an identity crisis until I swapped it for a Victron Blue Smart IP22 and suddenly everything just worked like it was designed in the same decade as my batteries.

@RiverFinn and @Cleggy83 make solid points. One thing I'd add from personal experience on my widebeam — don't overlook the temperature compensation issue. A lot of older shore power chargers will automatically adjust voltage based on temperature sensing, which is fine for lead-acid but actively harmful for lithium. If your charger's temp probe is still connected and nudging the charge voltage up during cold winter moorings, you could be pushing beyond what your BMS is comfortable with.

Worth checking whether your charger even has an option to disable temp compensation — some do, buried in the settings menu. If it doesn't, that's another reason to bite the bullet and replace the unit entirely rather than bodging the existing one.

What charger are you currently running? Might help narrow down whether it's worth persevering with or just binning it.