measuring battery drain

Grant Lenahan glenahan at
Wed Sep 5 08:11:16 EDT 2007

"drain" is the amount of electricity (current, not voltage) that is  
being drawn by the car all the time when it is off.

You simply open up the ground lead and insert an Ammeter (amp-meter) so  
that the electricity flows from the battery through the meter, to the  
ground lead to the car.  Actually it flows in reverse, btu that's  

You can only do this for low currents. Never turn anything on that  
draws a lot of power with a portable meter in line like this. And for  
heavens sake dont try to start the car. Your meter and its wires will  
be toast. Literally.

Read the meter. It will be in milli-Amps (Amps/1000). For power,  
multiply by the battery voltage, which better be around 12.5-13 volts.

Circuits 101.  The best summary I know of basic electrical circuits is  
the preamble to "the radio amateurs' handbook" - the official  
publication of the ARRL - the ham club.  or any physics 101 textbook.

On Sep 4, 2007, at 11:08 PM, Huw Powell wrote:

>> For some of us who don't understand how to measure "battery drain",  
>> could
>> someone please explain.
> Not to be snippy, but have you tried:
> num=50&hl=en&q=measuring+battery+drain&btnG=Search
> If you want to get fancy, restrict the search to this site (I think you
> type "" as well, to do that, but I never remember it
> right).
> -- 
> Huw Powell
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