Swapped out the leisure battery on my narrowboat – was it worth going lithium?

Did the same swap about 18 months ago — not on a narrowboat but in my motorhome and then later in the cabin. Same principles apply though, so worth chipping in.

Short answer: absolutely worth it. Long answer: it depends entirely on what you were putting up with before.

My old AGM setup on the motorhome was a constant battle. Monitoring state of charge was guesswork, I was always nursing it above 50% to avoid killing it early, and by year three it was a shadow of itself. Swapped to a pair of Fogstar Drift 100Ah cells wired in parallel and it was like a different vehicle. Full usable capacity, no babying required, and the weight saving was genuinely noticeable.

The one thing I'd flag for narrowboat use specifically — temperature. If your battery compartment gets properly cold in winter (and on a canal boat it will), make sure your BMS has low-temperature charge cutoff. Charging lithium below freezing is the one thing that'll genuinely damage the cells. Worth checking what protection your BMS actually offers rather than just assuming.

Also — what inverter/charger are you running? Some older units don't play nicely with lithium charge profiles. A Victron MultiPlus sorted that headache for me, though it's not a cheap fix.

Would be interested to hear how you're getting on with solar input as well — boat life seems like a brilliant use case for a decent MPPT setup given you're often sitting moored in open water with decent sky exposure.

What capacity did you go for in the end?

@MountainHermit interesting timing on this thread — I'm actually weighing up exactly this swap on my narrowboat right now.

Few questions if you don't mind:

• Did you need to upgrade your alternator setup when you went lithium? I've heard the charging profile can be brutal on older alternators without a proper DC-DC charger in between
• What BMS did you end up going with?
• How are you finding it in winter — do lithium cells really suffer that badly below 5°C when you're trying to charge them?

I've been looking at Fogstar Drift batteries as they seem decent value for the capacity, but not sure whether to trust them long-term on a boat where humidity and vibration are constant issues.

Currently running a pair of 110Ah AGMs and they're frankly knackered after two seasons. Feels like the right moment to make the jump.

@ForestDweller what's putting you off pulling the trigger? Is it the upfront cost or are there specific narrowboat considerations worrying you?

I made the swap on my motorhome first before committing to anything on a boat, which helped me understand the basics without the added complexity of a marine environment. The one thing I'd flag that's different on a narrowboat is battery placement and ventilation — though obviously LiFePO4 is much safer than AGM in that regard anyway.

Also worth asking: are you running a BMV-712 or similar battery monitor? With lithium the state of charge readings are actually useful for once, unlike trying to guess with lead-acid. Made a big difference to how I manage things day-to-day.

What's your current setup — 12V or 24V system? And are you looking at Fogstar or one of the other options?

@ForestDweller one thing specific to narrowboats that doesn't get mentioned enough — your alternator charging profile matters a lot. Most older boat engines run a standard lead-acid profile which will technically charge lithium but absolutely hammers the cells over time and voids most warranties.

Worth fitting a proper DC-DC charger (Victron Orion-Tr Smart is what I use) between the alternator and your lithium bank. Adds cost, yes, but protects the investment.

Also consider your BMS cutoff behaviour on a boat — if it trips unexpectedly mid-cruising season it can kill your nav electronics at a bad moment. Get a decent battery with a sensible BMS, not the cheapest Fogstar option, tempting as the price is.

Done properly it's solid. Done hastily it's an expensive headache.

@SaltyHiker raises a genuinely important point that catches narrowboaters out. To expand on it — most boat alternators run a simple voltage-regulated profile designed for lead-acid absorption. Shove a lithium bank on there without a proper DC-DC charger (a Victron Orion-Tr Smart is the go-to) and you're either undercharging massively or potentially damaging the alternator through sustained high current draw, since lithium will happily pull everything the alternator can produce until it's full.

In my shepherd's hut setup I faced similar issues with solar controllers originally spec'd for AGM. Had to reconfigure the absorption/float parameters entirely on the Victron MPPT once I moved to Fogstar Drift cells.

For narrowboats specifically, also check your BMS disconnect behaviour — if the BMS trips whilst underway, a sudden open-circuit load can spike and kill your alternator diodes. Worth fitting a battery-protect or alternator protection relay to handle that gracefully.