When to change your battery
It’ll be obvious when your battery is flat: the central locking may not work and the engine won’t turn over. However, it’s not always easy to know when the battery needs to be replaced. Once the car has been started (via jump leads/jumper cables, bump started or battery trickle-charged) take the car for at least a 20-minute run to charge the battery. Turn off the engine and restart it the next morning. If it’s flat again you need to investigate further.
First, check the battery leads are secure. Then check the battery’s state of charge by either looking at the indicator eye (not present on all batteries), sampling the electrolyte in a battery hydrometer (not possible on sealed batteries) or perform a battery load or drain test with a suitable meter. If you need to change your battery, Haynes will walk you through all of the necessary steps.
All cars are slightly different, so if it is time to change your battery, use our before you begin checklist, and find your car for specific instructions.