[helluvaengineer96]

Two words... Thermal runaway...

A sealed battery can have this happen just as easy and a pressure release or cap will open, venting the hydrogen, hopefully into a well ventilated area..

Thermal runaway is when a battery is charging and over heats lowing resistance and the battery sucks in more current, gets hotter, lower resistance, and the battery suck in more current......

Out door telco cabinets have blown up from this occurring. (Non venting cabinet in the winter... a little spark.....)

I was sitting in the hot tub and this crossed my mind: Do seal lead-acid batteries vent hydrogen when they charge/discharge?