General Motors parasitic draw formula

Rudy Technician Utah Posted   Latest  

I remember GM had a formula that gave a rough estimate of how long a battery can sit before being depleted.

Anyone remember the formula?

0
Helpful
Mark Technician
Wisconsin
Mark
 

Here is the attachment.

+5
Ð Awarded
Helpful
Thanks
Rudy Technician
Utah
Rudy
 

Mark- Thanks for that. Although that is not exactly what Im looking for. What Im looking for is the formula they used to make that chart. I vaguely remember it had something to do with reserve capacity or ampere hours.

0
Ð Awarded
Martin Instructor
British Columbia
Martin
   

Rudy, It was in the battery usage table for each vehicle. Reserve minutes divided by 4, so 118/4 =29.5 mA maximum allowable drain. (Or 118 x 25%) However, in reality most were around 7-10mA with no excess draw. The usage chart seems to have been dropped. Envoy/Trailblazer 600 CCA 78 series 6Yr Reserve Capacity Rating 115 min 115x 25% = 28.75 mA. The normal draw on those 7 ma. Full-sized…

0
Ð Awarded
Rudy Technician
Utah
Rudy
 

Martin- I know you are well versed with all things GM, I distinctly recall there was a formula for determining approximately how long ( how many days or hours)a battery would last at a given mA discharge rate. I was certain they published such a thing. Maybe Im wrong and confusing them with another OE.

0
Ð Awarded
Martin Instructor
British Columbia
Martin
 

Hi Rudy. There is/was a formula, but I haven't looked for or seen it in some years. Just like the laminated chart siting in front of me, that lists typical draws for ignition on and lights on for cars and trucks. As battery technologies changed and in the case of the sheet I'm looking at, the results might well be non-applicable with current technologies. I'll take a look around and see if I…

0
Ð Awarded
Mike Diagnostician
Ontario
Mike
   

Have a look at this site. batterystuff​.​com/kb/tools/peuke… It might be the formula you are looking for. Regards, Mike

+1
Ð Awarded
Helpful
Stephen Technician
Tennessee
Stephen
 

Thanks for that link. I didn’t know to fudge AH capacity for differing current draws.

0
Ð Awarded
Rudy Technician
Utah
Rudy Resolution
   

Alright gents, I found it. I had to do the leg work on my own. This TSB is old but I think the formula still relevant. TSB# …A' Excerpt: Here are some rules of thumb that might help relate parasitic drains to how long a battery would last on a parked vehicle. The Reserve Capacity (RC) rating multiplied by 0.6 gives the approximate available ampere-hours (AH) from full charge to…

+5
Resolution Ð Awarded
Helpful
Thanks