Do not work on a physically damaged battery
Swelling, cracking, leaking, punctures, severe corrosion, unusual heat, or a burnt smell are reasons to stop. Isolate the battery as recommended by its manufacturer and use an appropriate recycling or service route.
Protect your eyes and skin
For serviceable lead acid batteries, appropriate eye and hand protection matters because electrolyte is corrosive. Work in a suitable ventilated area and follow the safety data and manufacturer instructions for the battery.
Avoid sparks and short circuits
Batteries can deliver very high current. Remove conductive jewelry, use suitable tools, and keep metal objects from bridging terminals.
Lithium batteries need special caution
A damaged or failing lithium ion cell can enter thermal runaway. Do not puncture, crush, heat, or improvise charging methods for lithium packs.
Use the correct charger
Match the charger to the battery chemistry, voltage, and manufacturer requirements. Incorrect charging can damage a battery and create a safety hazard.
This safety overview is educational and cannot replace the instructions for your specific battery, charger, vehicle, or device.