Why does my car battery keep going flat?
A battery that keeps going flat is usually caused by one of three things — an ageing battery that no longer holds charge, a charging system fault such as a failing alternator, or a parasitic drain where something keeps drawing power with the car switched off. Testing the battery, charging output and current draw identifies which.
Signs of an electrical fault
- The battery keeps going flat, or the car is slow to crank
- The battery or charging warning light is on
- Headlights dim at idle or flicker
- Electrical accessories work intermittently
- Blown fuses that keep blowing
- Several warning lights come on at once
What does auto electrical work cover?
A car’s electrical system includes the battery, alternator and starter motor, the wiring and fuses, lighting, and the sensors and modules that run the engine and safety systems. Faults can be as simple as a corroded terminal or as involved as a damaged wiring loom.
How do we find electrical faults?
Electrical problems reward methodical testing. We test battery condition and charging output, measure current draw with the car switched off, check voltage drops across circuits, and read fault codes from the vehicle’s modules. Wiring diagrams then let us trace the fault rather than replace parts in hope.
Lights and roadworthiness
Headlights, brake lights, indicators and number plate lights are checked during a roadworthy inspection. If you’re preparing a car for a roadworthy, it’s worth having any lighting faults fixed beforehand.
Questions worth asking your mechanic
Whoever works on your car, these questions help you understand the job and the quote:
- Did you test the battery, the alternator output and the parasitic draw?
- Is the battery the right type for my car (for example, AGM for stop-start)?
- Does anything need to be reset or coded after the repair?
From our workshop
Recent jobs photographed at our Sunshine North workshop.
Frequently asked questions
How long does a car battery last?
It varies with climate, battery type and how the car is used. Lots of short trips and long periods parked shorten battery life. A battery test during a service shows how it's holding up.
My car has stop-start. Does it need a special battery?
Often, yes. Many stop-start vehicles need an AGM or EFB battery, and some need the new battery registered to the car's computer.