Reasons as to why Car Batteries die.

Presuming that your battery isn’t nearing the end of its life cycle, there are several things that can cause the battery to deplete.

1. Lights left on: This one happens all the time, of course. Many newer vehicles have a timer that shuts the headlights off after a minute or two if you forget and leave them on, but if your car doesn’t have this feature, you can easily walk away and leave the lights on for hours until they completely drain the battery.

If this keeps happening, try to get in the habit of making a mental note of whether you have the lights on or not. If it’s daytime and hard to tell whether they’re burning or not, check the switch on the dashboard. Make a Post-Its reminder for yourself, if necessary, because completely draining the battery for any reason will shorten its life.

2. Bad alternator: This is by far one of the most common causes of a dead battery. The alternator has a finite service life, and on many vehicles, it’s going to fail within 150,000 km. A failing alternator won’t charge the battery while you’re driving or may work intermittently before it fails completely.

If you suspect the alternator might be on its way out, keep an eye on the dashboard ammeter to see if it shows a charge (or look out for the warning light).

3. Corrosion: Your battery cables and terminals can become corroded with time, which will usually show up as a fluffy, powdery white, or greenish-white deposit around the terminals. This is often why many car batteries die.

The good news is that it’s fairly easy to clean corrosion from battery terminals and cables, using a stiff wire brush. You can then prevent the problem in the future by using felt anti corrosion washers on the battery posts and a Vaseline-like dielectric grease on the posts and the cable clamps.

4. Old/weak battery: Sometimes it’s just the end of the line for a battery. As the battery’s performance dwindles, it will turn the engine over slower. It might not be able to power the radio or other accessories for long before being exhausted, either.

Check the purchase date on the battery, if the battery is nearing the end of its warranty phase, it’s probably time for a new one.

5. Too many short trips: An engine needs to run for 30 minutes or more for the alternator to really do its job and start replenishing the battery. If you do a lot of trips of ten minutes or less, or if your vehicle doesn’t get driven often, that can be enough to exhaust the battery or not recharge it sufficiently.

6. Parasitic drain: There are a couple of systems in your vehicle that will always put a very slight drain on the battery. For instance, the radio pulls a slight charge all the time so it can store radio station presents.

A parasitic drain, on the other hand, is something that’s enough of a draw on the battery to deplete it. It could be a dead short somewhere in the electrical system. These can be hard to track down and might require a technician.

Otherwise, make sure that things like the glove box light or dome light aren’t staying on and exhausting the battery. If you’re handy, you can use a test light or multimeter to check for parasitic drain yourself.

7. Extreme temperatures: Extreme cold and heat can take their toll on a battery, especially an older one. When it’s below freezing, that by itself can be enough to cut the efficiency of the battery’s chemical process by as much as 50%. You can’t do much about the weather, but on very hot or cold days, try to avoid running the radio or other accessories for long stretches without idling the engine.

8. Overcharging: Automotive electrical systems have a voltage regulator that’s designed to prevent the battery from over- or undercharging, but it still happens occasionally. An external battery charger can also lead to overcharging, although most feature an internal switch so that won’t happen. Overcharging means that the battery is “over gassing,” with the electrolyte cooking away and releasing oxygen and hydrogen gases. On older batteries with vented caps on the cells, this could mean exposing the plates and ruining the battery completely.

9. Charging system failure: Modern vehicles have a serpentine belt that uses the engine’s energy to power the AC compressor, power-steering pump and other accessories. A loose or failing belt can also cause the alternator to not work properly, although most serpentine belts have a spring-loaded tensioner to keep them taut. Checking the serpentine belt should be part of routine maintenance a couple of times a year.

10. Loose battery connections: After removing or installing a battery, it can be easy to not tighten the clamps sufficiently. Anything less than a firm connection can be enough to interfere with the battery’s performance. If you can grab the cable and clamp at the battery posts and wiggle them at all, they aren’t tight enough and need to be torqued down.