Bought a cheap 100Ah leisure battery off Facebook — worth reconditioning or just bin it?

Depends what type it is. If it's a flooded lead-acid, there's a chance with some desulphation cycles. AGM? Probably not worth the hassle unless it's testing above 50% capacity.

I've rescued a couple of flooded batteries with a proper smart charger doing a reconditioning cycle — Victron IP65 has a decent mode for it. Took a few cycles but one came back to about 70% of rated capacity. Not perfect but fine for non-critical loads in the cabin.

That said, Facebook batteries are a lottery. Half the time the stated capacity is fantasy even when new, so "100Ah" could mean anything.

Few things worth checking first:

• Specific gravity with a hydrometer if it's flooded — tells you a lot
• Resting voltage after a full charge (should be 12.6-12.8V minimum)
• Load test it properly, not just a voltage check

If it's sitting below 11V it's likely sulphated badly or has dead cells. Dead cells = skip.

What are you planning to run off it? If it's just a few lights and phone charging, even a degraded battery might do the job for a season. Wouldn't trust it for anything critical though.

What charger have you got? That'll affect whether reconditioning is even an option.

@GrumpyBuilder slap a Victron Battery Sense on it first — no point flogging a dead horse (literally) until you know what voltage it's sitting at after 24 hours off load.

@CotswoldCruiser good shout on testing first. Once you've got your readings, run it through a proper desulphation cycle if it's flooded — I used an old CTEK MXS 5.0 for this on a knackered 110Ah I pulled from a skip. Took three full charge/discharge cycles before it started behaving itself. Ended up with about 70% usable capacity, which was fine for my cabin backup setup.

AGM I wouldn't bother personally. The internal structure's usually too far gone by the time they're being flogged cheap on Facebook.

Worth checking the date code stamped on the case too — anything over 4-5 years old is probably a lost cause regardless of type.

Rescued a battered 110Ah flooded battery from a boat I bought years back — looked absolutely grim, sitting at 10.8V and smelling like a chip shop. Ran it through three desulphation cycles on an old CTEK MXS 5.0 and it came back to about 70% capacity. Not glorious, but it powered my narrowboat's lighting and water pump for another two seasons.

The critical bit nobody mentions: check the electrolyte levels before you do anything. Half the "dead" batteries I've seen have just been bone dry. Top up with distilled water, let it settle overnight, then test and recondition.

If it's a sealed AGM and it's dipped below 10V repeatedly, honestly walk away — the plate damage is usually irreversible and you're just burning time you could spend sourcing a decent Fogstar or similar.