You're late for work and rush out to your car, only to find that it won't start. You know instinctively that your battery is dead. But how did this happen? There are five main causes of car battery drain or failure.
You’ve probably done this at least once in your life – you’ve come home from work, tired and not really thinking, and you’ve left your lights on or you haven’t completely closed your trunk. Then, in the morning, you have a dead car battery, and your car won’t start. Most new cars will alert you if you’ve left your lights on, but may not have alerts for other components.
Parasitic drain is due to components in your vehicle continuing to run after the key is turned off. Some parasitic drain is normal – your battery delivers enough energy to keep things like your clock, your radio presets and your security alarm operational at all times. Sometimes, though parasitic drain exceeds what is normal, and can cause car battery drain.
If your charging system isn’t working properly, your car battery can be draining even when you’re driving. If your lights, radio, and other things are running off your alternator, your car battery will drain and you could end up with car battery failure. Then you’ll be stranded at roadside with a stalled car that needs a boost. And even then, bad charging will drain your car’s battery.
Defective alternator diode
If your alternator has a bad diode, your battery can drain. The bad diode can even cause the circuit to charge even when the engine is shut off. Then you end up in the morning with a car that won’t start.
If your battery is old, it might not hold a full charge any longer. If your car isn’t starting consistently, it’s possible that your battery is just worn out. You should usually replace your battery every 4-5 years, so if your car isn’t starting consistently, and your battery is old, this should be the first thing you consider.
Assuming that the cause of the battery drain is not human error, you will need the assistance of a qualified mechanic who can diagnose your electrical problem and determine if it is the battery or something else in the car electrical system.