What's everyone actually running as a backup when your main bank dies mid-winter?

Lost power on the narrowboat last February — three days of grim grey skies, Renogy 200W panel pulling virtually nothing, and my Fogstar 100Ah LiFePO4 down to 8% before I'd even boiled the kettle. Victron SmartShunt was giving me the full horror story in real time. Not ideal when you're moored in the middle of Cheshire with no shore power hookup anywhere nearby.

Since then I've been putting together a proper backup plan rather than just hoping the sun shows up. Currently looking at a second smaller battery — maybe a 50Ah — kept on a trickle from a dedicated solar input, totally separate from the main system. The idea being it's only touched in emergencies, not quietly drained by the fridge overnight.

Has anyone done something similar, or is there a smarter approach I'm missing? Curious whether people go for a second isolated bank, a petrol generator they hate the noise of, or something else entirely. Also wondering if a proper shore power inlet is just the sensible long-term answer for winter months specifically.

@CarlCole97 that February grey stretch was brutal — I remember it well from the motorhome.

My backup salvation ended up being a Jackery Explorer 500 tucked under the bed. Not glamorous, but it's kept the 12V fridge ticking and phone charged when my main Victron/Fogstar setup has been sulking.

The real game-changer though was wiring in a B2B charger so I could top up from the vehicle alternator whilst driving between sites. Even a short 20-minute run nudged things up meaningfully.

One thing I'd genuinely recommend — a small Honda EU22i generator stashed in the boot locker. Winters in the cabin taught me that solar is brilliant until it absolutely isn't. Sometimes you just need brute-force electrons from petrol.

What's your mooring situation like? Shore power hookup even occasionally would change everything for you.

@CarlCole97 nightmare scenario, been there on the boat myself. My fallback is a battered old 40Ah AGM I keep tucked under the stern, purely for emergencies — yes it's heavy and inefficient but it's never once let me down and cost me practically nothing secondhand. Pair that with a decent 12V leisure battery charger running off a small Honda EU22i genny and I can at least keep the essentials ticking — lights, bilge pump, phone charged. The genny's the real insurance policy honestly. Burns maybe a litre overnight on eco mode. Not glamorous but February on the cut with no power is genuinely dangerous, so I'd rather have something ugly and reliable than nothing at all. Worth keeping a jerry can stashed too — learned that the hard way.

Cheers @CarlCole97, sounds like a proper horrible situation. I've got a similar narrowboat setup and after a near miss two winters back I now keep a small Honda EU22i genny stashed in the bow locker — not glamorous but it'll top up the bank and run the immersion for an hour without fuss. Crucially I also fitted a basic 12V car battery on a separate circuit purely for the bilge pump and navigation lights, so even if the main LiFePO4 is flattened I'm not in genuine trouble. The Honda's not cheap but it starts first pull in the cold which is worth every penny when you're moored somewhere grim in February with no shore power nearby. @RustyCaptain's AGM idea is solid too — belt and braces is really the only sensible approach on the cut.

@CarlCole97 been caught out similarly on the cabin — January, two days of solid overcast, Victron SmartSolar doing absolutely nothing useful.

What saved me was keeping a small 20Ah sealed lead-acid purely as emergency reserve, wired through a Victron Battery Protect so nothing can accidentally drain it. Bit old school but it's bombproof and costs next to nothing.

Also worth looking at a small Honda EU22i or similar inverter genny as true last resort — I resisted for years but it's genuinely transformed winter confidence on the boat too. Run it an hour, top everything up, job done.

The other thing I'd say: pre-winter load audit. Sounds obvious but I didn't realise my bilge pump float switch was drawing phantom current until I actually checked. Saved me several Ah per day.

Really feel for you @CarlCole97 — February on the cut with a dying bank is miserable.

My backup on the boat is a small Honda EU22i petrol genny paired with a decent battery-to-battery charger. Not glamorous but it's saved me more than once. The key thing I've learned is don't wait until you're at 8% to break it out — I set a rule for myself that anything below 30% SOC during a prolonged grey spell and the genny goes on immediately. Top up little and often rather than one desperate rescue charge.

Also worth considering a small 30-40Ah starter battery completely separate from your main system, just enough to run a basic light and phone charging. Keep it isolated so nothing can accidentally drain it.

What charger are you running alongside the Renogy? Sometimes the controller settings are leaving performance on the table.

Good timing on this thread — I went through something almost identical last March, which pushed me into finally sorting a proper layered backup.

What actually saved me was a Honda EU22i paired with a small 20Ah AGM "emergency only" battery kept fully charged and isolated from the main system. When the Fogstar bank is struggling, I can run the Honda for 2 hours, top the AGM right up, and that covers critical loads — 12V fridge, phone charging, a bit of lighting — without touching the depleted main bank at all.

The key thing I'd add that nobody's mentioned yet: keep your backup physically separate from your main Victron system. I had a configuration issue that meant my "backup" was silently being drawn down alongside the main bank. Wasted months thinking I had a safety net. Test it properly in isolation before you actually need it.

Great thread, @CarlCole97 — narrowboat winters are brutal for this exact reason.

I keep a compact Honda EU22i petrol genny aboard specifically as the "bank saver" for those soul-destroying grey spells. Not glamorous, but an hour's run through a decent charger gets you enough to cook and keep the lights on without the stress. Pair it with a decent transfer switch and it becomes almost seamless.

The other thing worth considering is a small 12V leisure battery as a dedicated "essential services" reserve — completely isolated from your main bank. Fridge and bilge pump only. Saved me more than once on the Cotswold Water Park moorings.