5 Reasons Your Car Battery Drains

The top 5 things that will drain your battery
5 reasons your car battery drains

You're late for work and rush out to your car, only to find that it won't start. The headlights are dim and the engine simply start. You realise that your battery is dead. But how did this happen? There are five main causes of car battery drain or failure.

Human error

You’ve probably done this at least once in your life – you come home from work, tired and not really thinking, and left the headlights on or didn't completely close the trunk. Overnight the battery drains, and in the morning your car won't start. Many new cars alert you if you’ve left your lights on, but may not have alerts for other components.

Parasitic drain

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, radio presets, and security alarm operational at all times. However, if there's an electrical problem, a parasitic drain can exceed what's normal and deplete the battery. 

Parasitic drains below 75 milliamps are normal, but any parasitic drain over 75 milliamps will drain the battery quickly. The most common causes of a parasitic drain are under hood lights, trunk lights, headlights or glove box lights that do not turn off when the door is closed. Relay switches that are stuck in the “on” position can also cause a battery to drain.

Bad charging

If your charging system isn’t working properly, your car battery can drain even while you’re driving. Many cars power their lights, radio, and other systems from the alternator, which can make the battery drain worse if there's a charging problem. Then you’ll be stranded at by roadside with a stalled car that needs a boost. And even then, bad charging will drain your car’s battery. A professional mechanic will be able to diagnose what's causing a charging problem.

When an alternator is not pushing out enough voltage, which should be between 13.5 and 14.5 volts, the battery will drain quickly. This is especially true if you play the radio and lights while driving. Once the car battery drains completely, the headlights and radio will not operate. The car will stall and not start again until the battery is charged.

Defective alternator diode

A car alternator recharges the battery and powers certain electrical systems. If your alternator has a bad diode, your battery can drain. The bad diode can cause the circuit to charge even when the engine is shut off, and you end up in the morning with a car that won’t start.

Old battery

If your battery is old, it might not hold a full charge. If your car consistently won't start, it’s possible that the battery is worn out. You should generally replace your car battery every 4-5 years. If your car isn’t starting consistently, and your battery is old, battery replacement should be the first thing you consider.

Having a battery that won't hold a charge is frustrating, and figuring out what's causing the problem can be tricky. 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 problems and determine if it is the battery or something else in the electrical system.

To avoid the above, take note of these points:

1.Make sure all of the interior lights are off and that nothing is left on that could drain the battery. You should also never leave the radio on for an extended period of time when you do not have the car running.

2.Keep the battery clean. Use a dry rag to wipe off any dirt or residue near the terminals and connection areas. An unclean battery can sometime be the cause of its drainage.

3.Check to make sure that the cable connections to the battery are tightened and clean. A loose or dirty connection can cause drainage and other problems to the battery.

4.Use a portable car battery charger or volt meter to test and charge the car’s battery if it is below performance level. You can purchase a charger at a local automotive retailer and then use the charger’s jumper cable to test the wattage of the battery.

5.Take your car into an automotive specialist if you continue to have problems with the battery or if you have recurring trouble with the engine turning over. If you replaced the drained battery with a new one yourself then you should make sure you know the cause of the drainage so the problem does not continue.

Jemimah Abimbola Posts

I am passionate about writing, I love to read and am also a big foodie.