Anyone else running a second-hand leisure battery bank? Share your setups and what you paid

I've been putting together a small off-grid setup for my shed/workshop on a tight budget and decided to go the second-hand route for batteries rather than buying new. Picked up three 110Ah AGM leisure batteries from a local caravan dealer's clearout — £25 each — and wired them in parallel for a 330Ah bank at 12V. They're a few years old but tested reasonably well with a load tester, sitting around 70-75% capacity by my reckoning.

Paired them with a 200W panel I got off Facebook Marketplace for £40 and a Victron MPPT 75/15 (the one splurge, bought new for £55). The whole lot charges up fine on a decent day and runs my LED lighting, a small radio, and occasionally a 12V compressor fridge without too much drama. Winter's been the real test though — shorter days and the batteries not holding quite as well in the cold.

My worry is how long these batteries will last before they start dropping off noticeably. I've been keeping them above 50% state of charge as much as I can to try and extend the life, but I'm realistic that they're not going to last forever at this price point. Has anyone found a reliable way to assess second-hand AGMs before buying, beyond a basic load test? And is anyone else mixing old and new batteries in a bank, or is that always a bad idea?

Hey @MidlandsExplorer, nice setup! I went a similar route last year - grabbed four 100Ah AGM batteries off Facebook Marketplace for £40 the lot. Bloke had used them in a motorhome but upgraded to lithium. Tested them all with a proper battery analyser before handing over the cash - crucial step that, don't skip it!

Two came back with decent capacity (~85Ah actual), one at around 60Ah, and one was basically toast. Still, three usable batteries for £40 is hard to argue with.

My top tip: always ask why they're selling and how old the batteries are. Leisure batteries from caravans often have surprisingly gentle use histories compared to ones from solar setups that've been hammered through deep cycles daily. Worth factoring that in when you're hunting around. 👍

Four mismatched AGMs from a caravan graveyard, two of them quietly dying — living the dream 🔋

Honestly though, biggest lesson I learned: test internal resistance before you buy, not after you've lugged them home in the back of a Fiesta. A £15 battery tester from Amazon saved me from three very expensive paperweights last month.

@MPPTFan's Facebook Marketplace point is solid but also check local caravan/motorhome breakers — I got a pair of decent Varta 110Ah units for £40 the pair because a dealer just wanted shot of them before winter storage season.

Running them through a Victron BMV-712 so at least I know exactly how badly they're performing at 2am. 📉