Car battery: the complete guide

How a car battery works

The battery stores electrical energy chemically and releases it as a powerful burst to crank the engine. It also powers the car when the engine is off and smooths the alternator’s output.

• Rest voltage of a healthy battery: about 12.6 V
• Under 12.2 V it is roughly half charged
• Below 12.0 V it is being damaged by deep discharge
• CCA = cold cranking amps at -18 °C

How long does a battery last?

Four to six years is typical. Heat is the biggest killer — hot climates and engine-bay heat shorten life. Frequent short trips that never fully recharge also age batteries quickly.

Testing the battery

Measure rest voltage 30 minutes after driving, then load-test it. A battery that reads fine at rest but collapses under load is failing. Test the charging system too — a weak alternator kills batteries.

Replacing the battery safely

• Turn the car off and remove the key
• Disconnect the negative (−) terminal first, positive (+) last
• Remove the hold-down bracket and lift the battery out
• Clean the tray and terminals
• Fit the new battery, connect positive (+) first, then negative (−)
• Re-enter the radio code and let the idle relearn if needed