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[deadFX]

this FX is something special. any ideas why one of my batteries went dead. 2 days ago fully charged, today 26V measuring from the pins. some sort of internal fuse. BMS not responding. no bulging or swelling. some sort of Zero defect?

[TheRan]

26v exactly, or at least close to it? That's a really weird voltage because the cells are ~4.15v fully charged so that doesn't come out to a whole number, it'd be 6.2 cells you'd be measuring. If it was 6 of them then they'd be way overcharged at 4.3v, if it was 7 they would have been discharged all the way down to 3.7v which shouldn't happen in 2 days of sitting. That said you also shouldn't lose a bunch of cells either so who knows, just the only thing I can think of is a short that bypasses a load of them.

If that's not the case and you are measuring the voltage of all the cells then they're discharged below 1v and the battery is trashed. I would have thought there was some sort of protection to prevent them from being actively discharged (so, under some sort of load) to that low though, and again 2 days isn't anywhere near long enough for it to self-discharge that much.

[Auriga]

A lot of this depends on where you're measuring. If you're using the two smaller pins in the center of the connector, that goes through the BMS and a bad BMS can make that number weird. If you're using the two large outer ones, you shouldn't read anything outside the bike because the contactor should be open. That'd probably be a semi-welded contactor and maybe a bad bms.

I think it's more likely the battery is fine and you need another BMS. Happens sometimes. If you feel adventurous, you could remove the protector over the contactor and measure directly. Be careful though, that's full pack voltage and power!