Oftentimes when your battery dies it's because the headlights (or some other-powered feature) were left on after the car was shut off. So if you've left the headlights or radio on overnight then it's safe to say the battery is the problem. If you're not sure, there are a few things you can check.
Turn on the headlights
Are they dim? If the headlights are bright, chances are your battery is fine. If they're dim, it's likely the battery doesn't have enough charge to start the car.
Try to start the car
Obviously, you've tried this or you wouldn't be worried about a dead battery. But when you tried, did it turn over slowly? Or did it crank quickly? If it turned over slowly or not at all, it's likely that your battery is dead. If it cranked quickly it probably isn't your battery.
Most of the time you won't have an accessible battery jumper so you'll need to find another vehicle that you can use to jump your car. If no friends or family members are available, ask a stranger for help—many will be happy to assist.
You'll need to locate the battery in each of the cars. For most vehicles, the battery is located beneath the hood.
Use the hood release latch inside the vehicle to pop the vehicle hood. If you do not see the car battery after opening the hood, the battery might be under the back seat or in the trunk. Many foreign vehicles such as BMWs and Volvos locate the battery elsewhere.
Connect the jumper cables in the following order:
- Connect one red clamp to the positive terminal (+) of the dead battery
- Connect the other red clamp to the positive terminal (+) of the charged battery
- Connect one black clamp to the negative terminal (-) of the charged battery
- Connect the other black clamp to a piece of grounded metal, or as a last resort the negative terminal (-) on the dead battery
If your disabled vehicle doesn't start immediately, leave the assisting vehicle running, with cables connected, for 5-10 minutes. This will charge your battery a bit before starting.
If your vehicle still doesn't start, repeat this process and, before starting your car, have somebody rev the assisting car a bit by depressing the gas pedal slightly. This will temporarily send more current through the assisting vehicle's alternator to its battery and, ultimately, your vehicle.
Don't immediately shut off the engine or the battery may not have had enough time to recharge. Sometimes you'll need to keep the engine running for as long as 20 minutes. If you need to drive the vehicle, that should charge the battery faster as long as the alternator is working properly.