What happens to a Prius subpack when you overcharge it?

What happens to a Prius subpack when you overcharge it?
Opps! Cooked some prius subpacks

Well it happened again. I put my dual prius subpack on my 6A 75V solar panels for a quick recharge between the solar dish runs, and forgot it for several hours. When I finally remembered it, the black tape holding the subpacks together had nearly ripped apart and the cells swelled up with a lot of internal hydrogen pressure. Usually the subpacks are clamped tightly so they cannot swell, so they would vent the gas instead. I measured 140F between the packs, and submerged them in water to cool them.
Even after an overnight cool down, the subpacks were still swollen. I drilled six holes in two boards, to clear the locating tabs, so the clamping pressure would be uniform, and squeezed the subpacks together. Several hours of clamping, and the cells were back to normal shape, with no signs of any fluid venting.
I used the same packs to run my next canning run, and also to run a 30A 12V heater, and they seem to

Have been using the same dual pack in my lawn tractor for the last 2 years and they are working fine.
Some tough batteries for sure.