Anyone actually running a tiny house on second-life EV cells without spending a fortune?

Been piecing together my off-grid tiny house system for the past 18 months and I'm at the point where I need to commit to a battery bank. New LiFePO4 is still eye-watering — a 200Ah Fogstar Drift is around £400, so a proper 400Ah bank is already £800+ before you've touched an inverter or cabling. I keep coming back to second-life EV cells as the obvious budget route, but the information out there is all over the place.

I've got a rough 2–3kWh daily load (induction hob in short bursts, a 12V compressor fridge, LED lighting, laptop), fed by 800W of panels on the roof via a Victron SmartSolar 100/30. The plan is a 48V system so I'm looking at building a 16S pack from either CATL or BYD prismatic cells. Cells off eBay and AliExpress sellers seem to go for £40–70 per 100Ah cell depending on grade, which sounds almost too good — Grade A "tested" cells from some sellers, Grade B from others, and I genuinely can't tell what the grading actually means in practice.

Has anyone here capacity-tested second-life prismatic cells with something like a Junsi iCharger or even a basic ISDT unit before building into a pack? What sort of real-world capacity are you actually getting versus the rated spec, and are the Grade A/B distinctions from these sellers worth paying attention to or mostly marketing fluff? Also curious whether anyone's had issues with cell matching when you've got cells from different batches — I'd imagine internal resistance variance causes headaches down the line.

@LDVConvert I've been going back and forth on this exact thing for my static caravan setup. What puts me off second-life EV cells isn't the price — it's the testing headache. How do you actually verify capacity and internal resistance without proper equipment? I picked up a basic cell tester but I'm not confident I'm catching all the dud cells before they cause problems in the bank.

Did you find a reliable source in the UK? I've seen various eBay sellers but the descriptions are vague at best. Are people buying Nissan Leaf modules specifically, or is there something better suited for static installs where weight isn't really a concern?

Also curious whether a Victron SmartShunt handles the slightly inconsistent cells okay or whether you need something more sophisticated to babysit them.

@LDVConvert Running second-life cells on my narrowboat for two years now. Grabbed a batch of CATL prismatic cells off eBay — properly graded, not mystery lottery stuff.

Key thing nobody mentions: you need a decent cell tester before you commit. Capacity claims are optimistic at best. I top-balance mine manually before first use, every time, no exceptions.

@Julie1991 the "risk" is overstated if you match cells properly and pair them with a quality BMS — I use Daly, though JK is better if budget stretches. Victron Cerbo watching everything gives peace of mind.

Biggest gotcha is sourcing. Avoid anything without documented provenance. NKON and reputable UK dismantlers are worth the slight premium over random Marketplace listings.

Cost per kWh is genuinely half what new gets you. Not for everyone, but absolutely viable.

@LDVConvert I've got a static caravan setup running on second-life CATL cells I sourced through a UK EV dismantler — paid roughly £80/kWh compared to Fogstar pricing. Took a while to find a reputable seller but Facebook groups like "UK EV Battery Salvage" are worth trawling.

The bit nobody mentions enough: capacity testing before you commit. I used an ISDT BattGo to individually test every cell before building the pack. Binned about 15% straight away. Factor that wastage into your budget calculations.

@Julie1991 the quality concern is real but manageable — just avoid anything that can't tell you which vehicle the cells came from. Verifiable provenance matters massively.

Running through a Victron SmartShunt and it's been solid for 14 months. Would I do it again? Absolutely, but only if you're comfortable with the extra groundwork involved.

Really interesting thread — I went through exactly this decision for my garden office build last year.

Ended up sourcing Grade B CALB cells through a dismantler near Bristol. Paid around £180 for what became a 280Ah bank after I'd top-balanced everything with a bench power supply. Took a weekend and a fair bit of patience.

The critical bit nobody warns you about: capacity testing each cell individually before you build the pack. I used a Juntek battery tester — found two cells in my batch sitting at about 60% real capacity despite looking fine on resting voltage. Pulled them out, rest went together beautifully.

Running it through a Victron SmartShunt and Cerbo so I can actually trust the SOC readings. Eighteen months in, still hitting 95%+ of original capacity on the keepers.

@Julie1991 that individual testing step is probably what addresses your concern — it's the difference between a good batch and a nightmare.

JaneReid68 | 📍 Mid Wales | ⚡ Off-grid since 2019

@LDVConvert I've been running a 16S 280Ah bank of second-life CATL cells in my converted stone outbuilding for about 14 months now. Sourced them through a UK reseller rather than eBay — paid a bit more but got consistent capacity testing data with each cell. Biggest lesson: don't skip the individual cell capacity testing before you build your pack, even if the seller claims they've done it. I lost a fortnight chasing a balance issue that turned out to be two cells significantly underperforming. A decent cell tester is genuinely worth the investment. @ShedGenius is right that narrowboat vibration is a real consideration though — my static setup is obviously kinder to the cells. What's your typical daily consumption looking like? That'd help work out whether 280Ah is worth discussing for your situation.