Dangers

Which batteries are dangerous, and why

by Joe Miller

Most batteries are safe when used right. A few can start fires, burn through a child's throat or explode. Know which ones and what to do.

Emergency? Battery fire or a child swallowed a battery: call 911. Poison Help: 1-800-222-1222.

Ranked from most to least dangerous.

Lithium-ion fires

Once thermal runaway starts it is very hard to stop.

Buy certified: e-bikes, scooters and their chargers should carry a UL 2849 or UL 2271 listing.
Never charge a damaged or swollen battery, or use a no-name replacement charger.
Charge on a hard surface, away from exits, and not while you sleep.
Throwing away a lithium battery in the trash can start a garbage-truck fire. Recycle it.

Every year thousands of children swallow button batteries.

The liquid inside is sulfuric acid: it burns skin and blinds. Wear glasses and gloves.
Charging makes hydrogen gas. A spark can make the battery explode, so charge in open air and connect the charger before plugging it in.
When jump-starting, make the last connection to bare metal away from the battery.
Lead is toxic: wash hands after handling.

Alkaline leaks are caustic: wear gloves, clean with vinegar or lemon juice on a cotton swab, and wash hands.
9-volt batteries can short across steel wool or coins in a drawer and start a fire. Tape the terminals.
Homemade cells are the safest batteries here, but copper sulfate is poisonous and magnesium burns.

Tape the ends of lithium and 9-volt batteries before you drop them off.

Checked November 11, 2026.