Let's Play "What is making my battery drain?"

In reply to iceracer :

A long time ago, in a mechanic's shop far, far away...

My memory was blank but wiki says 2.1 volt per cell on a 12 volt automotive battery.

iceracer said:

Anybody ever tested a battery with a hydrometer ?

Often. But I work on old stuff.

My memory was blank but wiki says 2.1 volt per cell on a 12 volt automotive battery.

Yep, and x6 cells means 12.6, usually 12.65 fully charged. Anything above that is a 'surface charge' that will dissipate gradually.  

If you have OL/open/infinite resistance from the positive to the negative cable with battery disconnected, I wouldn't expect it to light up a test light anyway. I'd suspect the battery first. Looks like you're going that way so update if it turns out there's still something else wrong with it. 

Also, using a meter set to amps on a modern car to find a draw is sorta risky (to your meter fuse). Lots and lots of cars will momentarily go past 10 amps when you open the door or otherwise 'wake up' the car. A lot of procedures for finding parasitic draw involve waiting for 30mins for the car to 'settle' or go to sleep before actually starting your testing, and if you wake it up again you get to start over. 

I diagnosed a parasitic draw on an 02 GMC Yukon last week. In that case it was an on-site free diag for a family member with no money so I got as far as finding out it was related to a 50a MBEC fuse which feeds a 25a and a 30a circuit breaker which feed power seats and right side power windows. I wasn't able to replicate the issue quickly enough to know which one was causing it so for now he has no power seat, no power windows on right side, and a truck that starts in the morning.  

In reply to Stampie :

Why hadn't I ever thought of this?  This is awesome!  I need to do this on my Boxster.  I have to charge it regularly or else....  My miata too.  

The 996 and 944 (the oldest with worst wiring), not nearly as bad.

In reply to AnthonyGS :

Sorry I made a long list of things to do for you. I can't claim credit. I'm sure it's been mentioned here and I remember an old timer (I think Brad from my first job working on Volvos) showed me the trick. 

Stampie said:

In reply to AnthonyGS :

Sorry I made a long list of things to do for you. I can't claim credit. I'm sure it's been mentioned here and I remember an old timer (I think Brad from my first job working on Volvos) showed me the trick. 

If it helps resolve the issue, it'll be worth every moment invested.  I'm taking a half day off work Friday and this will go to one of my higher priorities because eating new batteries alive is too expensive. 

Pro tip:  Make up a pigtail and install a 2.5A blade fuse between the ground lead on your meter and chassis ground if you are using your meter to detect a drain using the "pull fuses" method.  This way if you accidentally draw too much current  during testing you blow a 2.5A blade fuse instead of the tough to source 10A fuse inside your meter.  

Real life experience:  Two cars with parasitic drain.  95 Eclipse GSX - factory amp was bad, isolated that, swapped it for a different one, went from 2 days of sit time before the battery was flat to 4 weeks.  Easily identified with Meter and Fuse technique detailed above.

Second car was a 2002 Corvette.  These are tougher because you need to put modules to sleep before you can start testing and you need a Tech II to do that.  Otherwise it can be up to 45 minutes before you can isolate circuits.  Got a Tech II, put modules to sleep.  No circuits showed unusal drain.  Battery was bad.  Replaced it and problem went away.

Now I keep anything I dont drive frequently on a battery tender.  Horrible Freight version is fine.  For a once a week car you are probably on the bubble for needing a battery tender.  A good battery and warm weather is fine, a questionable battery and cold weather and you are asking for trouble.  

In reply to iceracer :

Yes a giant battery on a US submarine....  zero stars, not recommended.

Update: swapped in a new battery last night. Voltage at 12.5X. I have to be out of town for the next 4 days so I can't try to find the parasite yet. But we'll get to see how much she drains in that time.

Update: After sitting from evening of Tuesday 2/25 to evening of Monday 3/2 the new battery lost .4 volts - down to 12.1. Earlier that day I had purchased both a circuit light and the cheapo HFreight digital circuit tester that you plug into the fuse slots.

Using the light bulb I probed the tops of all the big amp fuses and got nothing. Additional research will happen this weekend.

In reply to Dr. Hess :

Yes a Fluke or similar will show the mA draw current.

"The typical parasitic battery drain is 7-12mA with a maximum recommended drain of 30 mA."

Sparkydog said:

Update: After sitting from evening of Tuesday 2/25 to evening of Monday 3/2 the new battery lost .4 volts - down to 12.1. Earlier that day I had purchased both a circuit light and the cheapo HFreight digital circuit tester that you plug into the fuse slots.

Using the light bulb I probed the tops of all the big amp fuses and got nothing. Additional research will happen this weekend.

Put the test light in series with the negative terminal.

Probing the fuses will tell you nothing.

APEowner said:

Statistically, bad batteries are more common than parasitic draws.

Every German car I've ever owned is laughing.