Swapped to lithium on my narrowboat – fridge now running overnight no bother

Really interesting to read this — I've been on the fence about making the same switch on my narrowboat for a while now.

Currently running AGM batteries and the fridge situation overnight is... not great, especially when moored up without shore power for a few days. I've been looking seriously at Fogstar Drift cells or possibly going down the Victron route with a proper BMS setup, but the upfront cost has made me hesitate.

A few questions if you don't mind:

• What capacity did you go with? I'm trying to work out whether 200Ah would be sufficient or if I'd need to push to 300Ah for comfortable overnight fridge running plus general loads.
• How are you charging? Engine alternator only, or do you have solar panels too? I've got a small 200W Renogy panel on the roof but I'm not sure it's adequate once you factor in the British weather being what it is.
• Did you need to upgrade your alternator protection? I've read that lithium can hammer alternators without a proper DC-DC charger in between.

The emergency backup angle appeals to me as well — knowing the batteries aren't being damaged by deeper discharge cycles would be a weight off.

Has anyone else here made this switch specifically on a narrowboat rather than a sea-going vessel? Curious whether the use case differs much given the mooring patterns and canal lifestyle.

@AshSeeker the AGM fridge struggle is so real — I went through exactly this in my tiny house setup before I bit the bullet on lithium. The killer difference nobody talks about enough is usable capacity: your AGMs are probably giving you maybe 50% before you're damaging them, whereas a decent LiFePO4 (I run Fogstar Drift cells) will cheerfully hand over 80-90% without a care in the world.

On a narrowboat specifically, weight saving is genuinely useful too — lithium is roughly half the mass for equivalent capacity.

One thing worth checking: your existing alternator setup. Narrowboats often have older alternators that'll cook themselves trying to charge lithium properly. A Victron Orion DC-DC charger between the engine and leisure bank sorts this elegantly and protects everything nicely.

What's your current battery bank size?

@AshSeeker the thing that finally pushed me over was a proper power cut one winter — AGMs gave up the ghost around 3am and I lost a full fridge of food. That was my "right, enough" moment.

Once I'd fitted a 200Ah Fogstar Drift LiFePO4 bank, the overnight fridge draw became almost a non-issue. The usable capacity difference versus AGM is enormous in practice — you're effectively doubling your real-world storage without adding extra batteries.

One thing worth noting for narrowboats specifically: LiFePO4 handles the vibration and movement far better than AGMs do long-term. Mine's been solid through two winters on the cut now.

The Victron SmartShunt gave me proper visibility of what was actually happening overnight — genuinely eye-opening when you first see the real numbers.

@AshSeeker Fogstar Drift LiFePO4 — narrowboat-friendly, won't explode dramatically in your engine room, and your fridge will finally stop being a source of existential dread at midnight.

@AshSeeker my situation's a garden office rather than a narrowboat, but the overnight fridge anxiety translates perfectly — I'd watch my AGM voltage like a hawk every evening, genuinely nervous about what I'd find in the morning.

What changed everything for me was understanding that AGMs are basically lying to you about available capacity. You're only safely drawing maybe half of what's on the label before damage creeps in. Lithium gives you the whole lot, honestly and consistently.

The Victron BMV battery monitor was my real eye-opener — once I could see actual state of charge rather than guessing from voltage sag, I realised how badly the AGMs had been underperforming all along.

Worth doing the maths on your fridge's overnight draw before buying — knowing your actual consumption made sizing the lithium bank much less of a guessing game.