Anyone actually saved money going secondhand LiFePO4, or is it a false economy?

Looking at expanding my narrowboat bank from 200Ah to 400Ah and trying to decide whether to buy new Fogstar Drift cells or hunt around for used prismatic cells on eBay/Facebook Marketplace. New 280Ah cells are sitting around £180-220 each for decent grade A stock, so a 4S pack isn't cheap.

I've seen used 272Ah and 280Ah EVE cells going for £60-90 each with varying cycle counts claimed — anywhere from "barely used" to "pulled from an EV pack." Problem is there's no way to verify what you're actually getting without a proper capacity tester, which I don't own yet. Is the saving worth the gamble when you're mounting this in a boat with limited ventilation and no easy swap-out access?

Has anyone actually gone down the secondhand route and done proper capacity tests on arrival? What did you use — a Juntek, a Neey active balancer, something else? And what percentage of rated capacity would you consider the cutoff before rejecting a cell?

Smudge_6508 | 847 posts | ⚡ Solar Addict

@ExFirefighter I've gone both routes on my van build and a static cabin setup. The honest answer is it depends entirely on the cells' history, which you'll rarely get truthfully from private sellers.

What I'd suggest: if you do go secondhand, insist on capacity testing results before parting with cash. A good seller will have them; a dodgy one won't. Anything below 80% original capacity is already borderline for a boat application where you're cycling regularly.

The narrowboat use case specifically worries me slightly - you're in a damp environment with vibration from the engine. New cells with a proper warranty give you peace of mind that's worth something tangible there.

Personally I saved about £180 going secondhand on my cabin bank but lost six months of faff. Your time has value too! 🛶

AlisonHughes | 1,203 posts | ⚡ Solar Addict

@ExFirefighter One thing nobody's mentioned yet - provenance matters enormously with secondhand cells. Ex-telecom cells from proper suppliers like Fogstar's used stock or Niche Batteries' graded cells are a very different proposition to random eBay prismatic cells where you genuinely have no idea how they've been treated or what BMS they were paired with.

For a narrowboat specifically I'd be slightly cautious - the damp environment means you really want confidence in those cells. If you do go secondhand, insist on capacity test results, and budget for doing your own full cycle test before committing. A cheap cell tester is worth every penny.

Personally I landed on graded new-old-stock as the sweet spot between cost and peace of mind. What's the price difference you're actually looking at per Ah?

LesPhillips | 312 posts | 🔋 Off-Grid Enthusiast

Bought a set of secondhand CATL prismatic cells off Facebook Marketplace for my garden office build — saved about 40% versus new. Two years on, still holding capacity well. But I did my homework first: capacity tested every cell with a proper charger before building the pack, checked for physical damage, and only bought from someone who could demonstrate discharge curves.

The risk isn't the chemistry — LiFePO4 is robust — it's buying blind from someone who doesn't know what they're selling. Narrowboat use is relatively gentle cycling so aged cells can still serve well there.

@AlisonHughes makes a fair point about provenance though. EV pull-outs are a lottery. Cells from a known solar install with logged history? Much lower risk than mystery eBay listings with zero background.

AndyWilliams | 412 posts | ⚡ Solar Addict

Worth adding to what @AlisonHughes was getting at about provenance - on a narrowboat specifically, I'd be extra cautious with secondhand cells. The constant vibration and movement accelerates any existing internal degradation that you simply can't spot visually. I picked up some "grade A pulls" last year that capacity tested beautifully on the bench but showed alarming internal resistance after a few months of canal use.

That said, I wouldn't write off secondhand entirely. Facebook Marketplace occasionally has cells from solar installs that have barely cycled - those are genuinely worth chasing. Ask for the BMS history data if they have it.

For 400Ah on a liveaboard though? Personally I'd stretch to new Fogstar. The warranty alone is worth the premium when you're living on the boat.