Battery dying? Dead battery? How to test for a parasitic drain or draw with meter. Identify problem., by DontJerryRig-It on YouTube. 2 min 52 s.
- Video length
- 2 min 52 s
- Time to do it
- 1 hour
- Difficulty
- Medium
- Steps
- 8
What you need
Steps
Charge the battery fully first, because a weak battery gives confusing readings. Then switch off the ignition, lights, radio and any phone chargers, and close all doors, the boot and the bonnet.
Latch the door switches so the car thinks the doors are shut. On most cars you can flip the latch with a screwdriver, which stops the interior lights coming on and waking the electronics.
Set the multimeter to DC amps on the 10A range and plug the red lead into the 10A socket. Use the 10A setting only, since a lower range can blow the meter fuse.
Loosen the negative battery clamp and lift the cable off the post. Touch one probe to the battery post and the other to the cable clamp so the meter sits in line between them.
Wait 30 to 60 minutes without touching anything. Modern cars keep modules awake for a while after shutdown, and a real drain only shows once they go to sleep.
Read the meter. Around 0.02 to 0.05 amps (20 to 50 milliamps) is normal. Anything above roughly 0.08 amps means you have a drain worth chasing.
Pull one fuse at a time and watch the meter. When the reading drops to normal, that circuit is your problem. Note the fuse number and put it straight back before moving on.
Check the parts on that circuit: interior lights, boot light, glovebox light, aftermarket radio or alarm, and any relay that stays warm. Fix the fault, then repeat the test to confirm the draw is gone.
Tips and common mistakes
Never crank the engine with the meter in line, because the starter current will destroy it.
Keep your tools away from both battery posts at once to avoid a short and sparks.
Do not open doors or press buttons during the test, as that wakes modules and skews the reading.
A glovebox or boot light that never goes out is one of the most common causes of a flat battery.
Questions
What is a normal parasitic draw on a car battery?
Most cars settle around 20 to 50 milliamps once the modules sleep. Above about 80 milliamps is usually enough to flatten a healthy battery in a few days.
Can I do this test with the negative cable still connected?
No. The meter has to sit in series between the post and the cable, so the cable must come off. A clamp meter around the cable is the exception and needs no disconnection.
Why does my meter read zero or show nothing?
The internal fuse has probably blown, usually from a spike when you reconnected the cable. Check or replace the meter fuse and start again on the 10A range.
This guide was drafted from the video's details and general task knowledge. It has not been checked against the full video. Check the video and relevant product instructions before following a procedure. Report a correction.
