A battery that goes flat once can be bad luck: lights left on, a door not quite closed. A battery that keeps going flat has a cause, and it is almost always one of three things.
1. The battery is worn out
Batteries lose capacity with age, and heat, lots of short trips and repeated deep discharges speed that up. A worn battery may still start the car on a warm afternoon but struggle after a cold night. A proper battery test under load shows whether it can still deliver what the engine needs. Checking the voltage alone is not enough.
2. The battery isn’t being charged
If the alternator, drive belt or charging connections have a fault, the battery slowly runs down while you drive. You may see the battery warning light, dim lights or a car that is fine after a long trip but flat after a few short ones. See alternator warning signs.
3. Something is draining it while the car is parked
Every modern car draws a small amount of current when it is switched off, for the clock, the alarm and the memory in its control modules. A parasitic drain is when something draws more than it should. Common causes include:
- A boot, glove box or courtesy light that stays on.
- Aftermarket installations such as alarms, tracking units, dash cams and sound systems connected to a permanent power supply, or connected badly.
- A control module that does not “go to sleep” after the car is locked.
- A sticking relay or a short in the wiring.
Aftermarket installs are very common in South Africa, from tracking units required by insurers to alarms and dash cams. If the battery problems started soon after something was fitted, mention it. It is often the fastest route to the cause.
How a battery drain is found
The vehicle is locked and left until its modules go to sleep, which can take a while on some cars. The current draw is then measured. If it is too high, circuits are isolated one at a time until the drain drops, which shows where to look. The fault is then traced along that circuit to the component or wiring responsible. Guessing and replacing parts is how people end up on their third battery.
Information that helps
- How long the car stands before it will not start: overnight, a few days or a couple of weeks.
- How old the battery is, and whether it has been replaced recently.
- Anything fitted or repaired just before the problem started.
- Whether any light, fan or noise continues after the car is locked.
If you fly out of O.R. Tambo and leave the car parked for a week or two, a small drain that does no harm overnight can easily leave you with a flat battery when you land. That pattern is a strong hint that the drain, not the battery, is the problem.
Disconnecting the battery to stop a drain can reset radio codes, window settings and other memory on some vehicles. Check your owner’s manual first, and never disconnect the battery with the engine running.
Battery drain testing in Kempton Park
We test the battery and charging system and trace parasitic drains at your vehicle. Tell us the pattern of the problem and anything fitted recently. See our auto electrical repair service, or starting and charging faults if the car will not start right now.
Next step
Need help in Kempton Park? See our auto electrical repairs service or send your vehicle details to arrange a mobile assessment.
Related guides
- Car won’t start, just clicking? What it means
- Battery light on while driving? Alternator warning signs
- Car fuse keeps blowing? Signs of a wiring fault