Swapped to lithium on my narrowboat last summer – worth every penny or am I imagining it?

Not a narrowboat bloke myself — shepherd's hut and a motorhome — but swapped to lithium on both and the difference is night and day. Not imagining it.

The thing people underestimate is usable capacity. Your old lead-acid bank might've been 200Ah on paper but you were only ever safely using 100Ah. Lithium you're pulling 90%+ without a second thought. It's not magic, it's just maths.

Few things worth checking though:

• Did you sort your charging sources properly? Alternator, solar, shore power — all need to be lithium-compatible. Victron kit handles this well but plenty of people bodge it and then wonder why their BMS keeps tripping
• What's your BMS situation? Built-in or separate?
• Did you do anything about low-temp cutoff? Narrowboat bilges can get properly cold in January

The weight saving on a boat is actually more meaningful than people realise — lead-acid banks are absurdly heavy and it's all dead weight sitting low in the hull.

What cells did you go with? Proper branded (Fogstar do decent stuff for the price) or the usual eBay lottery? And what capacity did you end up at?

Suspect you're not imagining it but I'd want to know more about your setup before saying it's been done properly rather than just got lucky so far. Not trying to be funny, just seen too many installs on here that work fine until they really don't.

@BatteryTim yeah usable capacity is the big one nobody talks about until they've lived it

Had 200Ah of AGM on the motorhome. Thought I was sorted. Could actually only use maybe 90Ah before the voltage started tanking and the inverter got stroppy. Swapped to 100Ah Fogstar Drift and genuinely got more usable power out of it

People see the spec sheet and think lithium is expensive. Do the maths properly — cost per usable kWh over the cycle life and AGM looks mental expensive

Only caveat — BMS behaviour in cold weather can catch you out if you're wild camping in January. Learned that one the hard way somewhere in the Cairngorms. Not ideal.

Spot on @BatteryTim — and welcome to the forum, great first thread.

The capacity thing is only half the story though. What really converted me was the voltage stability under load. My motorhome used to dim its own lights when the compressor fridge kicked in — proper embarrassing. Swap to a 200Ah Fogstar Drift LiFePO4 and suddenly everything just... works. Fridge, inverter, the lot, without that voltage sag dragging everything down.

The other thing nobody mentions until it's too late is charge acceptance. Solar actually reaches the battery meaningfully now rather than tapering off early because the AGMs were already "full" on paper but genuinely half-spent.

Been running mine two winters now. No regrets whatsoever.

Weight savings on a narrowboat must be chef's kiss — my Fogstar cells turned my garden office into a floating palace, minus the floating and the palace.

@SolarNut floating palace is doing a lot of work there 😄

Quick question for the narrowboat folks — does the charging profile cause any headaches with older alternators? I'm asking because my shepherd's hut setup is static so I only deal with solar and a genny, but I keep hearing boats have grief with the alternator not liking the lithium charge curve.

Is a Victron BMS-to-alternator setup the standard fix, or are people using a DC-DC charger between the alternator and the bank? Curious what the actual real-world solution looks like rather than the theoretical forum rabbit hole I've already disappeared down for three hours this week.