Car battery keeps dying overnight — electrical drain?
My Camry battery goes flat every 2-3 days. New battery, alternator tests fine. I suspect there is a parasitic drain somewhere. How do I test for this?
A
This is a parasitic drain — something is drawing power when the car is off. Here’s how to find it:
Simple test: Fully charge the battery. Disconnect the negative terminal overnight. If the battery is still charged in the morning, the drain is in the car’s electrical system. If it’s still dead, the battery itself is faulty (even new batteries can be bad).
How to find the drain:
Get a multimeter set to DC amps. Connect it between the negative terminal and the negative cable with the car off and all doors closed. A reading above 50 milliamps means there’s a drain. Then pull fuses one by one until the reading drops — that tells you which circuit is causing it.
Common causes on Nigerian Camrys:
- Aftermarket car alarm draining power (very common)
- Interior light staying on due to a faulty door switch
- Aftermarket stereo or subwoofer wired incorrectly
- Faulty boot/bonnet switch leaving a light on inside
- Worn alternator diode (allows battery to discharge through alternator at night)
Check the boot light first — open the boot at night and see if the light is on. A stuck boot light is responsible for more dead batteries in Nigeria than people realise.