Anyone else using a small battery bank purely for emergency backup in a tiny house?

Running a 200Ah Fogstar Drift LiFePO4 as my backup for the tiny house — basically sits at around 80% most of the time doing nothing, just waiting for a grid outage. Victron SmartShunt keeping an eye on it. Wondered if this is a daft way to store it long-term or if LiFePO4 genuinely doesn't mind sitting idle at that SOC.

Main concern is whether I should be cycling it occasionally just to keep it "healthy" or if that's more of a lead-acid thing I'm overthinking. I do a manual discharge every couple of months down to about 20% then back up, but not sure if that's necessary or actually adding wear.

Anyone doing something similar? What SOC do you store yours at and do you bother with maintenance cycles at all?

Gibbo39 | 47 posts

@SOCGal Nice setup! One thing worth considering — keeping LiFePO4 perpetually sat at 80% is actually pretty sensible for longevity, but you might want to set up a scheduled cycle every few months just to keep the cells balanced. I do similar with my 100Ah backup bank; I've got a Victron MPPT on a small panel that gives it a gentle full cycle every 8 weeks or so, then settles back to storage voltage around 3.4V per cell.

The SmartShunt is brilliant for this — have you set up any alerts through the VictronConnect app for if it drifts outside your target SOC range? Gives you peace of mind that it's genuinely ready when the grid does drop out rather than discovering it's drifted down to 60% at the worst possible moment! 😄

MarineFrank | 134 posts

@SOCGal Curious about something — when you say "waiting for a grid outage," how long has it actually been waiting? On my boat the batteries get a proper workout daily, but I imagine a tiny house backup could sit there feeling quite unloved for months.

Do you have any kind of scheduled discharge cycle set

RM_Marine | 89 posts

@SOCGal Solid choice with the Fogstar Drift — decent cells in those. Just to add something neither @Gibbo39 nor @MarineFrank have touched on yet: have you sorted your transfer switching arrangement? A lot of tiny house folk I've seen cobble together a backup system but then realise during an actual outage that switching over smoothly is more faff than expected. Whether you're using a manual changeover switch or something automatic like a Victron MultiPlus handling the transition, it's worth testing it before you actually need it. Run a deliberate "drill" — kill the grid feed and see how everything behaves. You might catch surprises with certain loads dropping or restarting awkwardly. The SmartShunt won't help you there but it'll at least confirm your SOC is where you think it is when the moment comes.

BurnBen | 203 posts

Similar thing in my van build — battery just ticking over most of the time between trips. One thing I'd watch with the tiny house setup is temperature. If that bank is in an uninsulated space it'll derate in winter and you might get a nasty surprise when you actually need it. Had that exact issue first winter with my Fogstar before I sorted proper insulation around the battery compartment.

Also worth thinking about your inverter draw on startup — grid outages often happen during storms when you're running loads, so make sure your Victron kit is sized for that initial surge, not just steady state.

200Ah should be decent headroom mind, especially if you're only covering essentials.

T5Wanderer | 312 posts

@SOCGal Worth considering what your actual minimum runtime requirement is before committing to that 80% float strategy long-term. I've got a similar setup in my T5 — battery mostly idle between charges — and the question I kept coming back to was: what's the worst-case outage scenario I need to cover?

For EV charging specifically (if that's on your list), even a small top-up draw will chew through 200Ah faster than you'd expect. Prioritising critical loads only during an outage makes that bank stretch considerably further.

Also worth double-checking your Victron SmartShunt is correctly configured for LiFePO4 charge parameters — default settings sometimes assume lead-acid and the SOC readings drift over time if not dialled in properly.

SussexSolar | 447 posts

200Ah sitting at 80% doing nothing is basically a very expensive piece of furniture — have you considered a small trickle charge from a cheap Renogy panel just to keep the BMS happy and cycle it occasionally? LiFePO4 loves being used, not babied on a shelf. My cabin setup runs a deliberate weekly discharge cycle via a dummy load purely to keep the cells honest. Also worth checking your Victron SmartShunt is set to the correct Peukert exponent for LiFePO4 (closer to 1.05) — default settings assume lead-acid and you'll get wildly optimistic SOC readings during an actual emergency, which is precisely the worst moment to discover that.