Why does my car battery keep going flat? The 6 most common causes

A battery that goes flat once can be bad luck. A battery that goes flat every few weeks has a cause. These are the six we encounter most.

1. Only short trips After starting, a battery needs roughly twenty to thirty minutes of driving to recover. If you only drive ten-minute trips, you structurally put back less than you take out.

2. A parasitic drain A dashcam that keeps running, a badly wired towbar kit, an alarm or a module that never sleeps all draw current while parked. A healthy system draws about 20 to 50 milliamps at rest. Far above that and your battery is flat within a week.

3. The alternator undercharges An alternator should deliver roughly 13.8 to 14.7 volts with the engine running. Structurally less and the battery never fills, dying of chronic undercharge. Fitting a new battery solves nothing.

4. The battery is simply finished Most starter batteries last four to six years. After that the cold cranking performance drops far enough that it still starts in summer but not in winter.

5. The wrong battery type A stop-start car needs an AGM or EFB battery. An ordinary flooded battery is not built for the hundreds of extra start cycles and is worn out within eighteen months.

6. The new battery was never registered Many modern cars track battery age and wear and steer charging accordingly. If a new battery is not registered, the car keeps charging as if the old one were still fitted.

How do you know which one it is? By measuring. Resting voltage, charging voltage and quiescent current together tell almost the whole story. That is exactly what we do before replacing anything.