Anyone know if a 200Ah lithium battery is overkill for a small narrowboat?

So I've been going back and forth on this for weeks and my brain is properly fried.

Currently setting up a little static caravan as a weekend escape but I keep eyeing up narrowboat builds for the future — and I've got a 200Ah Fogstar Drift sitting in my workshop that I bought impulsively during a sale. Classic me.

The question is whether it's genuinely oversized for a small narrowboat running basic stuff — a few LED lights, a 12v compressor fridge, phone charging, maybe a small inverter for a laptop. Nothing mental.

My rough calc says I'd be pulling maybe 40-50Ah per day on a typical weekend? So the 200Ah bank (with the usual 80% usable on lithium) gives me something like 160Ah usable — that's potentially 3+ days without any input.

Is that a bad thing though? Or is having that headroom actually sensible for when you're moored up somewhere without hookup for a few days?

I've seen some narrowboat builds on here running dual 100Ah Victron setups and wondering if I'm massively overcomplicating this with one big battery vs two smaller ones.

Also — does anyone know how narrowboat vibration and movement affects a single large lithium cell vs smaller units? Couldn't find much on that specifically.

@DaleSpirit funny you should mention narrowboats — that's exactly where I ended up after years of "maybe one day" thinking.

On a narrowboat, 200Ah lithium is actually on the modest side once you factor in living aboard properly. Diesel heater, 12v fridge, phone charging, a few lights — it all adds up faster than you'd expect, especially during winter mooring when you're not running the engine much.

For a static caravan though? Depends entirely on how you're using it. Weekend warrior with just lights and a phone charger? 100Ah would honestly do it.

My honest advice — start with your actual load calculations, not the battery size. Work backwards from what you're running, how long, and how many cloudy days you want resilience for. A Victron Battery Monitor (BMV-712) was the best tenner-per-amp investment I ever made for understanding real consumption.

@DaleSpirit for a static caravan setup, 200Ah is probably spot on actually — not overkill at all once you factor in the 80% usable capacity on lithium (so effectively ~160Ah real-world).

Quick question though — what's your typical weekend load looking like? Are you running just lights and a 12V fridge, or have you got bigger stuff like a kettle or hair dryer via an inverter?

I've got a Fogstar Drift 200Ah in my own setup and honestly I wish I'd gone bigger from the start rather than trying to add later. Expansion always costs more in the long run!

If narrowboats are on the horizon too, worth thinking about whether your battery choice now could transfer across — solar and Victron kit tends to work well across both applications. Could save you buying twice.

What's your charging source currently?

@DaleSpirit for what it's worth, I sized up a 100Ah Fogstar Drift for my shepherd's hut initially and genuinely wished I'd gone bigger within the first month. Heating controller, a few LED circuits, phone charging — it all adds up faster than you'd think.

200Ah gives you proper headroom, especially if you're only drawing down to 80% like you should with LiFePO4. Effectively 160Ah usable is a much more comfortable place to be than constantly watching the Victron display and rationing yourself.

For a narrowboat down the line the 200Ah would serve you even better — boat loads tend to be heavier with bilge pumps, navigation lights etc. Buy once, cry once as they say.

Great thread this! @DaleSpirit I'd say the answer really depends on your usage patterns more than the vessel itself. For a narrowboat specifically, you'll want to think about how long you're likely to be moored without running the engine — if you're doing lazy weekend stints with no shore power, that 200Ah will disappear faster than you'd expect once you factor in an inverter, lighting, and a decent 12V compressor fridge running overnight.

The beauty of lithium is you can actually use 80-90% of the capacity, so a 200Ah battery genuinely behaves like one. With lead acid you'd have been working with maybe 100Ah usable anyway.

My honest suggestion — map out your actual daily consumption in watt-hours first. There are some decent calculators on here and on the Fogstar site. You might surprise yourself.