I don't get over here very often, but saw this thread and couldn't pass up sharing my experience.
I work on powersports stuff for my day job. Mostly ATV's, bikes, and side-by-sides. We used to sell/service Bad Boy MTV's (separate company from bad boy buggies which is owned by ez-go). They're now called "intimidator UTV". Anyway, the MTV I was messing with was a 48v electric. Eight 6v batteries, big ones-as I recall those batteries are about 75 lb each. So this guy brings one in and says it won't go. Very common complaint with electric carts. I hate them. Anyway, the state of charge "gauge" was showing "low" so I had him drop it off, we'd charge it overnight and then come back tomorrow & check it out. Fair enough he says. Pushed that heavy pile of trash into the shop, hooked the cord up to it, watched the charger and went home. Everything was going fine. Came in next morning, charger was "off" (it turns itself off when charge is complete). SOC indicator gauge says "full". Hmm. Well what's the problem? Guy said it wouldn't go. I climbed on, hit the throttle and it goes just fine, full power, full speed. Drove around the parking lot for about 30 minutes or so at varying speeds. Anyway, I was driving around and made a turn-at which time it lost all power, would barely pull itself. Nothing else unusual. SOC gauge says "1/2". Figured batteries were getting aged and probably time to replace them. Sat there for a minute, floored it, barely moves, and within a second a big kaboom. I was blown off of the seat, seat was broken off of it's mount, myself and the parking lot and the entire MTV was covered in battery acid, tons of smoke, some fire. I landed maybe 10 feet from the MTV, thankfully it was in a cold water-filled ditch which I used to wash the acid off of my face and head. Man it was cold. But at least I saved my eyesight.
Anyway by time I got it pulled back around to the shop, the cops show up wanting to know what the big boom was. Told them what happened, and asked who called it in. They said he had about 5 calls from different places-2 of them were about a mile away, said they heard an unusual explosion sound and they became concerned. That tell you anything?
One of the 4 under-seat batteries was completely black/charred. 6 others (2 under the bed, one under the nose, and the others under the seat) had all blown apart, completely. There was nothing left but lead plates and a bunch of acid. Washed what I could off and told the boss what happened, who called the owner.
To this day, I've not regained my hearing. About 50%. The accident happened about 5 years ago. I can no longer go out to the woods or the water and enjoy quiet because of the constant high pitched ring. I hate it.
What caused it? One of the 8 batteries (the black one) had an internal short apparently-or that's what the battery people (interstate) said, which overheated it-and ignited the hydrogen. What caused the others to bust? Dunno. They busted from inside out, not outside in as would be expected if a neighboring battery exploded.
What did I learn? Respect batteries-especially lead-acid. And I no longer work on electric carts, period. If that thing would've exploded inside the building, the whole back of the shop would have been damaged or destroyed, and I decided that we won't take that chance again.
