Car batteries tend to die at the most inopportune times. Sometimes you’ll get the usual warning signs, such as an engine that’s slow to turn over or an illuminated check engine light. At other times, you get no signs at all. That’s why it’s always a good idea to regularly have your battery tested. It’s also wise to keep a jump-starter on hand as an extra precaution.

If your battery is more than three years old, it may already have been time for a replacement. As for newer batteries, once you’ve ruled out obvious causes, such as having accidentally left the trunk, glove box, or car door open, you have to dig deeper. Here are three less common reasons for a dead car battery.

1. The alarm system

Car alarms installed by the automaker don’t usually cause trouble, but aftermarket alarm systems are a different story. Installed correctly, they draw a small amount of power and won’t drain your battery. Installed incorrectly, they can suck the power right out of your battery.

If you have an aftermarket car alarm, it should be one of the first things you check when your battery is unexpectedly low. The problem could be as simple as a frayed wire touching a metal part, causing an intermittent connection. If the alarm system is new, however, it might be a more complex problem that needs to be examined by the installer.

2. The stereo system

Another potential culprit is your car’s stereo system. Once again, it’s not usually those installed by the automaker that will drain your battery. It’s the aftermarket systems you can hear three cars down that tend to be trouble. The larger and more powerful the system, the greater the potential for battery drain.

To check if the stereo is the issue, simply disconnect your stereo system and see if that cures your battery woes. This will tell you whether the stereo is the problem, but figuring out exactly what needs to be fixed could be more challenging. It all depends on how your stereo was installed, and you may need the help of an experienced technician to fix the problem.

3. The car key

Once upon a time, car keys were metal objects that you had to turn in the door to unlock your vehicle. Today, many cars operate with proximity keys, which unlock the doors automatically once brought within a certain range. That’s a handy feature when your arms are full and your key is stuffed in your pocket, but also one that can cause battery issues.

A proximity-key receiver checks every signal at its frequency to see if it matches the vehicle. Any proximity key will trigger the system. If you’re parked for an extended period near the entrance of a parking lot, for example, where people with proximity keys in their pockets happen to walk by all the time, you might end up with a drained car battery. This won’t be true for every car, but hybrids are particularly susceptible to this issue.

It can be frustrating trying to figure out what’s draining your car battery. Looking into these three unusual causes right from the start will help limit that frustration and get you back on your way.

For more information about car battery issues, speak to an expert at your local NAPA AUTOPRO Service Centre.