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

I've got a 58ft narrowboat and I've been limping along with four 110Ah AGM batteries for the past three years. They're starting to sulphate and honestly I'm sick of the constant worry about getting them below 50%. Total usable capacity of around 220Ah is just not cutting it anymore, especially on longer cruises away from marinas.

I've been looking seriously at swapping to a 200Ah lithium setup — probably a couple of 100Ah LiFePO4 batteries with a decent BMS. Yes it's more upfront cost, but the usable capacity is basically the same as doubling my bank, and the weight saving alone would be noticeable on a steel hull. I'm currently running a 30A Sterling B2B charger off the engine and a 200W solar panel on the roof, so the charging side should be fine with a bit of tweaking.

Main thing I'm not sure about is cold weather performance. We moor up in the Midlands and it got down to -6°C last January. I know lithium cells don't like charging below freezing — has anyone had issues with this in practice, or does a halfway decent BMS handle the cutoff reliably enough that it's not a real problem?

Also wondering whether anyone's had grief with their 240V inverter setup after switching. I've got a 1500W Victron Multiplus and I'd love to know if anyone's had to reconfigure the charge profile significantly to get it playing nicely with lithium.

@Midge66 Not a narrowboat here but I've been through a very similar head-scratching process fitting out my shepherd's hut — ditched AGMs for a 200Ah Fogstar Drift LiFePO4 last spring and honestly can't believe I waited so long.

The weight saving alone was significant, but the real difference is just using the capacity properly rather than babying it to 50% like the old AGMs.

A few questions before you jump in though:

• Is your alternator a fixed voltage type? Lithium really wants a proper DC-DC charger (Victron Orion is what most people seem to recommend) rather than charging direct
• What's your solar situation?
• Do you have any existing battery-to-battery charging already fitted?

The upfront cost stings but over the lifespan it genuinely works out cheaper. What's your current charging setup?

Not a boat person myself — my lithium setup is for a garden office — but the principles carry over pretty well.

One thing worth flagging for narrowboat specifically: temperature management. Lithium BMS protection cuts charging dead below ~5°C, which matters if the boat sits unused in winter. Some Fogstar Drift cells handle this better than others, and Victron's systems let you configure a low-temp charge cutoff properly rather than just hitting a hard BMS wall unexpectedly.

Also worth checking your alternator situation. Standard boat alternators can fry themselves trying to charge lithium without a DC-DC charger (Victron Orion-TR Smart is popular for this). That's an added cost people often miss when budgeting the switch.

440Ah lithium would likely smash what you've got now for actual usable capacity. The AGM headaches really do disappear.

Great timing on this thread @Midge66 — I made the switch on my 62ft last spring and honestly wish I'd done it sooner.

The thing that sold it for me beyond the usual weight/capacity arguments was the flat discharge curve. With AGMs you're constantly second-guessing your state of charge, especially running 12v lighting and a pump. With lithium you've genuinely got usable power right up until the BMS cuts in.

One narrowboat-specific thing worth mentioning: vibration. Make sure whatever cells you go for are properly secured — canal running isn't exactly smooth and I've seen terminals work loose on poorly mounted setups. Also think carefully about your alternator — you'll likely need a smart regulator or at least a dedicated lithium charging profile, otherwise you'll cook your alternator trying to charge a battery that looks perpetually empty.

Happy to share what I went with if useful.

Running 200Ah of Fogstar Drift LiFePO4 on my narrowboat and it's been solid. One thing worth flagging that nobody's mentioned yet — check your alternator situation carefully. Most older narrowboat engines have unregulated or poorly regulated alternators that'll hammer lithium cells trying to bulk charge them. Either fit a proper DC-DC charger (Victron Orion-Tr Smart is what I used) between the alternator and your lithium bank, or get a decent external regulator sorted.

Also worth thinking about battery placement — lithium doesn't like being in an unventilated gas locker the way some people keep AGMs. Mine sit in the engine bay with decent airflow.

The weight saving over four 110Ah AGMs is genuinely noticeable on a narrowboat too. Trimmed mine noticeably.