A flat battery is a symptom
Replacing a battery may restore the vehicle temporarily, but repeated discharge usually needs diagnosis. The cause can be an ageing battery, a charging problem, something remaining awake after shutdown, poor connections or an accessory wired incorrectly.
What should be tested
A proper diagnosis checks battery condition, charging voltage, cable voltage drop and the vehicle's current draw after its electronic modules have gone to sleep.
- Battery state and capacity
- Alternator output under load
- Cable and earth voltage drop
- Key-off current draw
Information that helps
Tell the technician how long the vehicle sits, when the battery was fitted, whether accessories have been added and whether the problem began after other work. Intermittent faults are easier to find when the pattern is clear.
When to arrange help
If the vehicle needs repeated jump starts, the battery warning light appears, cables become hot or there is a burning smell, stop relying on jump starts and arrange electrical testing.