NiMH needs venting. "One inherent risk with NiMH chemistry is that overcharging causes hydrogen gas to form, potentially rupturing the cell. Therefore, cells h

NiMH needs venting. "One inherent risk with NiMH chemistry is that overcharging causes hydrogen gas to form, potentially rupturing the cell. Therefore, cells have a vent to release the gas in the event of serious overcharging" [0] [0] - https://en.wikipedia.org/wiki/Nickel%E2%80%93metal_hydride_battery https://en.wikipedia.org/wiki/Nickel%E2%80%93metal_hydride_b...