Anyone else running lithium on a narrowboat? Thinking of ditching my AGMs

Last winter really did it for me. I've got a 57ft narrowboat and I've been limping along with four 110Ah AGMs wired in parallel for a few years now. Two of them are basically dead weight at this point — won't hold a charge past about 40% capacity — and I'm at the point where I need to either replace like-for-like or finally make the jump to lithium.

I've been looking at two 200Ah 12V LiFePO4 batteries from a supplier on eBay (one of the better-reviewed Chinese brands, not going to name names yet) with a proper BMS, which would give me 400Ah usable at roughly 80-90% vs the maybe 180Ah I'm actually getting out of the AGMs right now. Running a 40A DC-DC charger off the engine alternator and a 30A MPPT from 400W of solar on the roof. The solar setup has been solid — it's the storage that's letting me down.

Main concern is the BMS cutting out in cold weather when we're cruising in January/February. Has anyone fitted a battery heating pad or just relied on the cabin staying warm enough? The batteries would be living in the back cabin, which does stay reasonably warm when the stove's going, but overnight it can drop a fair bit. Would love to hear what others have actually done rather than just what the spec sheets say.

Dave1983 | 847 posts

@Declan1985 Made the switch about 18 months ago on my 62ft and honestly wish I'd done it sooner. The usable capacity difference is night and day - I've got 200Ah of lithium and it genuinely outperforms what my old 440Ah AGM bank was giving me toward the end.

One thing worth factoring in for a narrowboat specifically is weight distribution. Lithium saved me probably 60-70kg which actually made a noticeable difference to how she sits.

Biggest practical tip: sort your alternator protection out before you do anything else. Lithium BMS cutting out under load can kill an unprotected alternator sharpish. A decent DC-DC charger between the alternator and the lithium bank is the proper way to do it - Sterling and Victron both do good units.

What's your current charging setup - solar, alternator only, shoreline?

Lefty92 | 847 posts

@Declan1985 Made the switch about 18 months ago on my 60-footer and honestly wish I'd done it sooner. The usable capacity difference is massive in practice - you're actually getting 80%+ rather than the AGM's 50% before damage kicks in.

One thing specific to boats that's worth flagging: make sure your BMS has a proper low-temperature cutoff. Bilge temperatures can surprise you on a bad January and you really don't want to be charging lithium cells when they're approaching freezing.

Also worth checking your alternator setup carefully - lithium's acceptance rate can cook an older alternator without a decent DC-DC charger in between. Sterling make a decent one that's popular on the cut.

What's your current charging setup? Solar, alternator, shoreline? Makes a difference to how you'd spec the new bank.

Worth noting lithium behaves differently on the cut vs a motorhome — engine alternator charging can be brutal on lithium without proper protection. Make sure you've got a DC-DC charger (Sterling or Victron Orion are the go-to choices) between your alternator and the bank, otherwise you'll cook your BMS or trash your alternator.

Also worth factoring in that narrowboats often sit unused for weeks. Lithium self-discharge is minimal so that's actually a win over AGMs in that scenario.

Fogstar Drift cells are popular for the budget build, or go Victron Smart Lithium if you want the full ecosystem integration. What's your current solar/charging setup like? That'll affect which way to jump.

FZO_Marine | 312 posts

@Declan1985 @CornishCamper raises a really important point about alternator charging — worth budgeting for a decent DC-DC charger (B2B) like a Victron Orion-Tr Smart rather than wiring lithium directly to your alternator. Narrowboat alternators often run continuously at tick-over which lithium will happily drain dry, potentially killing your alternator in the process.

Also worth considering: are you cruising seasonally or living aboard? If you're on the boat through winter and mooring up for extended periods, lithium's lower self-discharge becomes a genuine advantage over AGM. That said, don't forget lithium won't accept charge below roughly 5°C without a battery management system that handles low-temp cutoff — definitely something to factor in on a cold narrowboat bilge.

What's your current charging setup beyond the engine? Solar, shoreline, both?

DaleVicky | 203 posts

Not a narrowboat myself, but I run lithium in a shepherd's hut and also charge an EV off the same bank — so I know a thing or two about demanding loads hitting a battery hard.

@FZO_Marine and @CornishCamper are right to flag the alternator issue. What sorted it for most people I've seen tackle this is a decent DC-DC charger between the alternator and the lithium bank — a Victron Orion-Tr Smart is the go-to. Protects your alternator from the lithium's voracious bulk-charge appetite.

@Declan1985 also worth thinking about your BMS spec carefully. Fogstar Drift cells are popular right now and the pricing is genuinely competitive, but make sure whatever BMS you pair with them can handle the canal environment — damp and lithium aren't great friends without proper protection ratings.

What's your current inverter/charger setup?