BMW 735i Battery is dead Inspection at your home or office.

Common reasons for this to happen:

• Dead Battery: Batteries have a finite lifespan. Most last five years or so, while other batteries are heavy-duty and rated for more than this. All will eventually die and need to be replaced. This is a normal part of vehicle maintenance, and your battery, starter and alternator should be tested regularly to ensure that you’re not stuck on the side of the road with a dead battery.

• Car Lights Left On: With the advent of smarter automotive technology, this has become rarer, but it still occurs. If your car’s lights don’t have an automatic shutoff feature, they’ll stay on unless you physically turn them off. If this happens and the engine isn’t running, they’ll pull power straight from the battery, eventually killing it.

• Door Not Fully Closed: If your door is open, then the dome light will be on, and other interior lights may also be on. These lights draw their power from the battery if the engine isn’t running, and can quickly drain a battery.

• Dead Alternator: The alternator produces electricity while the engine is running, and is responsible for providing all the power needed for your engine, your accessories, and to recharge the battery. If the alternator dies, it won’t charge the battery, and all the power needs of your vehicle will come straight from the battery. Eventually, this will drain it completely, leaving you stranded.

• Bad Starter: It might not be the battery that’s the problem – if your starter has turned its last, your car won’t crank either. Again, regular maintenance can help predict starter failure.

• Failed Main Relay: Sometimes, everything in the charging system is perfectly fine, but your car still won’t crank. In this instance, the first suspect should be the main relay, since it controls the fuel pump and the car’s computer.