Oftentimes when your battery dies it's because the headlights (or some other battery powered feature) was 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.
You'll need to locate the battery in each of the cars.
You'll want to locate the batteries first so you can make sure you position the cars so that the jumper cables can reach both batteries.
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
Start the vehicle that will be providing a charge to the dead battery.
You can do this in the reverse order that they were attached, but it typically doesn't matter.
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.