Thread: Parasitic Battery Drain

You keep waking it up...

Originally Posted by SeanC

Drove 45mins home checked the battery drain. 13mA all good.
Turned on the interior lights to make sure the multi meter was working. 0.8A. Turned the lights out. 120mA.
Disconnected and reconnected the Neg a couple of times. Back to 1.2A.

Using an amp meter I have noted 1.2A - 2.1A from the negative cable during the period after turning the engine off when the systems are going through shutdown routines. This is normal.
So assuming your 1.2A continues beyond a reasonable time, perhaps one of the ECUs is not shutting down properly every time and staying "awake" and this is somehow triggered by battery disconnection.

Try taking readings at each fuse to narrow down the source using the little terminals on top of each fuse.
An easier way is to use an amp meter and a wire loop like this:


Another thought .... perhaps the original draining event was an improperly reconnected negative terminal.

Regards,
Scott

Hi Tombie,

I can leave the battery for disconnected for a week and still get 1.2mA. Hopefully everything should be asleep by then.

How can you get 1.2A with the battery disconnected? As soon as you connect it by any means to get a reading the car wakes up as Tombie said. That is normal.


You would need to check it with a clamp meter after it has gone to sleep and the handbrake light is off. Even opening the bonnet wakes it up so it needs to go to sleep with the bonnet open!


I had mine go to 5V over night without warning at Katherine Gorge after a very rough road a couple of days before. Once I managed to charge it the battery was OK again but I replaced it any way. I haven't had a problem since and that was in May.

Hi Bob,

I've been leaving the vehicle locked the bonnet open and the battery disconnected. I bridge the negative terminal and clamp with the multimeter to take a measurement.

Would taking a measurement this way wake the vehicle up?

The most telling thing is that if the battery is fully charged this afternoon and I leave the it connected it will be below half charged tomorrow.

If you are making a circuit by what you are doing it will wake up. If there is no circuit (the battery is not connected) there will be no amps, so you must be making a circuit to measure the amps. I assume from what you are saying that you are using a multimeter in series with the circuit to bridge the gap between the negative terminal and the negative cable.

Sean, you said 1.2mA in your post and I assumed you meant 1.2A.


1.2A would take over 60 hours to flatten a battery. 1.2mA would take 60,000 hours to flatten the battery. It is much more likely that the battery needs replacing, as did mine. You need much higher current draw to flatten the battery to 5 volts over night.

Bob. It should be 1.2A.

Overnight the charge drops from 12.6V to about 12.0V.

60 hours would be about be about right to flatten the battery below 5V. It was after 4 days that I found the battery was dead flat.