What Voltage & Current Readings When Checking Battery Drain?

**xJohnDoe001x** · 03-08-2013, 09:17 PM

What Voltage and current readings should I be reading with the engine off when I disconnect the positive cable and put the positive VOM probe on the battery positive terminal and the negative VOM probe connected to the Positive Cable?

Of course before I check I'll pull all fuses and disconnecting everything else except the ECM on my
'90 GMC Sierra, 5.7L TBI, 1/2Ton, 2WD
Sincerely Jon

**Steve** · 03-08-2013, 09:22 PM

What's your goal? To determine the output of your charging system or checking for the ability for the battery to hold a charge?

**xJohnDoe001x** · 03-08-2013, 09:43 PM

Originally Posted by Steve

What's your goal? To determine the output of your charging system or checking for the ability for the battery to hold a charge?

Thank you for letting me know that I did not make it clear that
I want to check the battery drain, with the engine off

**dpeter** · 03-08-2013, 10:22 PM

If there is ANYTHING using power no matter how small, you will get the same battery voltage between positive terminal and positive cable as you get from positive terminal and the negative terminal of the battery. As for current/amp draw.... no clue but to guess it should only be in the mili amp range. I may go check mine just for a base line because I am not having problems at present. I'll get back to you.

Well after checking, it seems theory does not match reality. Battery voltage is 12.45 and volts between battery post and cable is 10.7(cable disconnected) . Current or amp draw goes from 1.2 at first contact then to 0.6 for about 10 seconds and finaly drops to 0.07 and stays there. Measurements were take with a Fluke 89DVM

**xJohnDoe001x** · 03-09-2013, 01:04 PM

Great answer! I was stuck on the pre ECM car method where you do check for voltage and less than three volts is good when everything is disconnected.

You are right! theoretically all battery voltage should register?

The Engine Computer Module is always drawing a current, I suspect less when the engine is off.

**dpeter** · 03-10-2013, 08:46 AM

Forgot to consider A/C verses D/C. There are probably capacitors in play that would cause the open circuit voltage measurement taken between cable and battery terminal to be different than battery voltage.

**xJohnDoe001x** · 03-10-2013, 05:26 PM

You helped me get my head right earlier, I am now more interested in the amps but my Fluke 77's current checking capacity doesn't work, which is why I got it for $5 at a swap meet., so I have to decide to get it fixed or buy a new cheap one from Walmart for $20.