https://www.space.com/asteroid-could-hit-earth-in-september-2019.htmlYou would be 1,000,00,0000 more likely to get whacked by a cement truck on your way to the market. You have put severe constraints on the battery and that is the trick.
"Boom, Crack, Roar, Fizzle" in an RV Park
"What are those loud noises," asks the DW
"Aww nothing" you reply "Just the usual exploding batteries"
Hydrogen is explosive but severe gassing carries a particularly vile form of lead. Lead sulfate. Worry about that, not another Eniwetok Atoll