Checking for battery drain

[John Zuber]

Can anyone tell me how to properly use a multi-meter to determine if there is excessive electrical drain on the battery when vehicle is off? Do I just disconnect the negative from the battery and check between that negative cable and positive connection still hooked to the battery? In looking at the meter manual, would I be using the "resistance measurement" setting in doing this?



Or am I trying to place my meter between the battery positive post and positive cable (thus disconnected) and taking a "direct current (DCA) measurement" reading? What is the exact procedure? Thanks



:banghead:

 

[John G]

I haven't tried it, but I'm 99% sure this will work:



1. Use the current (amps) feature (not the resistance feature), and make sure that you have inserted the leads (wires) of the multimeter in the correct holes on the multimeter to measure current - they will be not the same pair of holes as for measuring voltage and resistance.



2. Disconnect one of the car battery from one of its cables (it doesn't matter which of the two terminals as long as you don't do anything really dumb, but let's say you choose to disconnect the cabe attached to the battery's negative term).



3. Now connect one multimeter lead to the battery's negative terminal (which has nothing else connected to it) and one to the connector on the cable that normally would be attached to the negative terminal (but isn't because you disconnected it) above. It doesn't matter much which of the two multimeter wires (red and black) you connect to the battery, if you do it one way the meter will show negative current and if you do it the other way it will show positive current.



4. The current you measure will probably be less than an amp, unless you have a light on.



Don't try this while starting the engine.

 

[John Zuber]

thanks...I did some more searching and what you describe is what I found. Found this:



http://www.youtube.com/watch?v=yFCT-YZbU5o



Thanks again for the help.

 

[scott degroot]

Set the meter to read amps, disconnect the negative battery cable and then hook the meter to the battery cable end and then the battery. At first you may have about a 2 amp draw that will go away almost instantly and then gradually go down. Keep in mind that it will take about 45 minutes for everything on the vehicle to shut down so hook the meter up and come back in an hour. Make sure the keys aren't in the ignition and that all the doors are closed, also if there is an underhood light make sure you unplug it. Maximum acceptable current draw once the system has gone to sleep is .050 milliamps. Anything over that and you can have a dead battery overnight depending on the battery.



This process can be very tedious on Fords if you don't have a scanner being that the system will stay awake for 45 minutes after the key is shut off and removed however if you have the scanner you can force the system to sleep..



When I test these I actually leave the drivers door open but close the door latch with a screwdriver so that I can access the fusebox and if there is a draw once the sytem is asleep you can start pulling fuses one by one until you find the fuse that stops the draw, from there you have to find all that fuse controls and go from there.

 

[John Zuber]

Thanks...makes sense.