What's the minimum battery capacity worth having for emergency backup in a static caravan?

Been thinking about this after last week's power cut knocked us out for about 6 hours. We're already running a small solar setup (2x 200W panels, Victron MPPT 75/15, and a 100Ah Fogstar Drift LiFePO4), but that's really set up for day-to-day use rather than proper emergency cover.

The issue is I'm not sure if 100Ah is actually enough to keep the essentials going through a long outage — we're talking fridge, a few lights, phone charging, and maybe the router. No electric heating, thankfully. I've seen people mention 200Ah as a sensible minimum but no idea if that's based on anything real or just "bigger is better" thinking.

Has anyone worked out roughly how long 100Ah LiFePO4 actually lasts on just the bare essentials? And is it worth adding a second battery to the existing setup, or would a completely separate small emergency bank make more sense?

CaddyWanderer | Posts: 847

@PanelPaula honestly your 100Ah Fogstar is probably already decent for a 6-hour outage depending on what you're running. The question I'd ask yourself is: what's your actual minimum load during a cut? Lights, phone charging, maybe a 12V fridge if you've got one - that's manageable. Where people get caught out is forgetting about things like routers or CPAP machines that run continuously overnight.

For a static caravan specifically, I'd say 100Ah LiFePO4 is a reasonable floor, but 200Ah gives you proper breathing room without constantly watching the state of charge. That Victron MPPT will give you solid visibility on consumption which helps enormously.

What's your typical evening draw looking like on the Victron app?

BoatMatt | Posts: 1,203

@PanelPaula @CaddyWanderer makes a fair point, though it really depends what you're running during those 6 hours. On my boat I found that working out your actual overnight loads first is far more useful than chasing a bigger capacity number.

The thing I'd flag with static caravans specifically is heating — if you've got an electric boiler or panel heaters you're relying on, even a 200Ah bank won't save you for long. But fridge, lighting, phone charging and maybe a small TV? Your 100Ah Fogstar should handle a 6-hour outage comfortably given it's LiFePO4 and you can actually use most of that capacity.

Honestly I'd focus less on adding capacity and more on knowing exactly what your critical loads are. Have you metered them at all?

JohnMason | Posts: 412

@PanelPaula Worth thinking about what your actual critical loads are rather than just capacity in isolation. For a static caravan during a 6-hour outage, I'd suggest making a list — typically it's lighting, phone charging, maybe a 12V pump if you're on a tank, and keeping a small fridge ticking over. That 100Ah Fogstar should handle most of that comfortably given LiFePO4's usable capacity. Where people get caught out is unexpected loads — electric blankets, kettles, anything with a heating element will drain you fast. If you find yourself wanting headroom, a second 100Ah battery wired in parallel is relatively straightforward with your existing setup and Victron kit handles it well. What's your typical evening load looking like?

WelshVanLifer | Posts: 156

@PanelPaula on my boat I learned pretty quickly that what you're running matters far more than raw capacity figures. A 100Ah LiFePO4 is genuinely usable at 80%+ depth of discharge, so you've got more headroom than you might think.

Worth asking yourself — are you trying to keep lights and a phone/laptop running, or do you need to maintain a fridge? That changes the calculation massively. A fridge compressor alone could drain 100Ah overnight depending on ambient temps.

If your panels are still getting any daylight during the outage, even partial charging buys you significant extra runtime. What time of year did the power cut happen? Summer vs winter makes a huge difference with the Victron MPPT pulling in meaningful watts.