What's the minimum viable backup setup for a liveaboard boat?

Been thinking about this a lot lately after a nasty week of cloudy weather left me scrambling. Running a narrowboat full-time and my main bank is 200Ah of Fogstar Drift LiFePO4 fed by 400W of solar through a Victron MPPT 100/30. In winter that's just not enough when the panels are doing nothing useful for days on end.

Looking at what counts as a "minimum" fallback — not a full second system, just enough to keep the critical stuff alive. Fridge, bilge pump, a couple of LED circuits, phone charging. Probably 300-400Wh of actual usable capacity would cover me for 24-48 hours of essentials.

Currently mulling a small secondary battery (maybe a 100Ah AGM as a dedicated backup, kept at float off a cheap B2B charger) versus just a quality portable power station like an EcoFlow River or Bluetti. The portability of the latter is tempting on a boat — easier to top up shore power when you're at a marina.

Anyone else doing something similar on a boat or van? What actually works in practice when your primary system takes a hit in winter?

DodgyNomad | Posts: 847

@DaiYoung56 Cloudy weeks are the real test, aren't they! My absolute minimum recommendation for a liveaboard backup is a decent DC-DC charger wired to your engine alternator. Even a 30-40A B2B like the Sterling or Victron Orion means every time you're cruising you're topping up properly rather than relying on that dodgy three-stage alternator output direct.

Pair that with a small Honda eu22i or similar genny for genuine emergencies and you've covered almost every scenario. The genny doesn't need to run daily - just knowing it's there removes the anxiety enormously.

With 400W solar and 200Ah Drift cells you're actually better positioned than most - it's really just those brutal December/January weeks where you need the backup to earn its keep.

What's your current alternator situation? That'd shape my suggestions further.

YEL_Marine | Posts: 312

@DaiYoung56 Worth considering a small dedicated backup bank separate from your main system — even 50-100Ah of AGM kept at float purely for emergencies. The psychological value alone is worth it. That way if your main LiFePO4 hits low voltage cutoff you've still got lighting and a VHF radio without scrambling.

Also don't overlook your alternator as a backup charging source — if you've got a Beta or Lister engine ticking away, a decent B2B charger means a 45-minute run covers a lot of ground on grey days. I'd prioritise that over a generator personally, quieter and you're running the engine anyway for heating in winter.

What's your current engine setup? That'd shape my recommendation considerably.

OffGridAlan | Posts: 1,203

@DaiYoung56 Worth considering a small dedicated backup bank separate from your main Fogstar setup - even 50-100Ah of decent AGM kept at float via your alternator. That way if solar fails completely you've still got a genuinely independent reserve for critical loads.

Also, what's your engine alternator situation like? A proper B2B charger (Sterling or Victron Orion) means even a 30-minute engine run gives you meaningful charge. Combine that with strict load shedding - fridge off, LED lighting only - and you can stretch surprisingly far through a grim fortnight in November.

The narrowboat canal network is actually brilliant for this because you're often ticking over anyway moving between moorings. Don't overlook that free alternator time you're already burning! What are your actual critical loads during those cloudy spells?

DuctTapeDave62 | Posts: 2,156

@DaiYoung56 Good shout from @YEL_Marine and @OffGridAlan on the dedicated backup bank - I'd add that your engine alternator is arguably your most underrated asset here. A decent B2B charger (I run a Victron Orion) means even a 45-minute cruise tops things up properly rather than just trickling in. For genuine minimum viable, I'd say: your engine as primary backup, a small 4G-connected Cerbo or similar so you can actually see what's happening before it gets critical, and honestly just ruthlessly knowing your daily consumption number. Cloudy weeks catch people out because they're estimating rather than measuring. What's your actual daily draw looking like? That changes the answer considerably.

SaltyTrekker | Posts: 487

My shepherd's hut setup taught me the hard way — a cheap Sterling B2B charger off the engine alternator is the unsung hero nobody mentions until they're sitting in the dark eating cold beans.