Most car batteries last about three to five years. Heat shortens battery life more than cold, so batteries in hot climates often fail sooner; cold weather is simply when a weak battery finally cannot start the engine. Short trips, long periods of sitting and a weak charging system also cut battery life. A healthy, fully charged battery reads about 12.6 volts with the engine off.
Signs your car battery is dying
- Slow, labored cranking, especially on cold mornings
- Clicking when you turn the key, with dim dash lights; see car won’t start
- Needing a jump-start more than once
- A swollen or cracked case, or a rotten-egg smell
- Heavy corrosion on the terminals
- Battery age over four or five years (check the date code on the label)
Battery voltage chart
| Resting voltage (engine off) | Approximate state of charge |
|---|---|
| 12.6 V or more | Fully charged |
| 12.4 V | About 75% |
| 12.2 V | About 50% |
| 12.0 V or less | Discharged; recharge and load-test |
Voltage alone does not prove a battery is good; a load test shows whether it can deliver its rated cold cranking amps. With the engine running, about 13.5 to 14.7 volts means the alternator is charging; see bad alternator symptoms.
What shortens battery life
- High under-hood temperatures
- Repeated short trips that never fully recharge the battery
- Sitting unused for weeks, or a parasitic drain from a module or accessory that stays on
- Loose or corroded terminals and a slipping serpentine belt; see serpentine belt
- Deep discharges, such as leaving the lights on
How to jump start a car
- Park the running car close, turn both vehicles off and set the parking brakes.
- Connect red to the positive terminal of the dead battery, then red to the positive terminal of the good battery.
- Connect black to the negative terminal of the good battery, then the last black clamp to bare metal on the dead car engine, away from the battery.
- Start the good car and let it run a few minutes, then start the dead car.
- Remove the cables in reverse order and drive for at least 20 to 30 minutes, or charge the battery fully.
A jump-start that leaves warning lights on or the transmission shifting oddly is often a low-voltage effect that clears once the battery is charged; see limp mode.
Making a battery last
Keep terminals clean and tight, use a battery maintainer on vehicles that sit, and replace the battery with the correct group size and type; vehicles with start-stop systems usually need an AGM battery. For boat batteries, see how long lithium batteries last and our trolling motor batteries guide.
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