When being charged, or even when not in use, batteries may contain hydrogen gas and air in an explosive mixture. This gas can be ignited by naked flames from matches, cigarette lighters, sparks from short circuits caused by spanners or incorrectly connected jumper leads. Always disconnect the earth lead first and replace it last when removing or replacing batteries. This will minimise the risk of a short circuit between tools and vehicle frame.

Battery electrolyte contains sulphuric acid that can cause damage to the vehicle as well as eyes, skin or clothes if spilt or splashed. Wash or hose off acid splashes with a water and baking soda mixture to neutralise electrolyte in inaccessible spaces on a vehicle. If the eyes are splashed, flush with running water and seek medical help urgently.