How do you check for battery draw or whatever kills a battery when the car is off. I have another vehicle im working on that supposedly the alternator tests good but sometimes kills the battery overnight after a few months of having a new battery. Also is there anyway for the starter or alternator to be bad but tests good on the autozone off the car belt tester and cause this type of issue as for as battery draw or pulling juice overnight or the couple days it sits?

 

Good video below …do voltage drop and not pull fuses…a failed alternator diode can cause a draw so you can remove the B+ cable off the alternator to verify when having the multimeter in series with the disconnected battery cable…Max current draw is reserve capacity of the battery divided by 4…120 minute RC would be 30 mA max !!…make sure the battery is fully charged before testing…12.66 volts…and KNOW how to use your DVOM properly…ie…how to connect the meter leads when measuring mA vs. mV !!

 

How to check the diodes !!…make sure the DVOM is set to the one way diode setting.

 

You may want to move this to a different section in general it was mainly in reference to a battery draw i had on another vehicle. This helps me in future to check parasitic drain as well as bad alternator diodes. This is just me trying to learn how to perform a battery drain as well as test alternator diodes that test good from autozone. Im assuming you need the parasitic drain type of connectors to perform this procedure? My harbor freight alternator battery test light died after a few uses so i've found out their electronics are junk. On my corvette the volt gauge reads from 13.4-13.8 but the fuses under the hood would read 13.7 and 14.2 on some so im assuming my alternator is good.

Great im trying to help my friend with his vehicle kills batteries every few months or sometimes the next day. I think maybe it has a battery draw somewhere as it'll start fine then the next day not start. I tried switching alternators they still read bad on the car according to the associated load tester. Reads 12.6 volts and about 13.1 volts with the car running. I have the bosch premium reman 140 amp that tested good as well as the other alternator i had for the car according to autozones alternator tester off the car. The autozone employee suggests taking the car in to see if it tests bad on the car but one time i had a bad starter on another vehicle that would barely crank he tested it said bad battery put in a new battery and found out the starter had died. Once installed they wouldn't take back the battery they sold me according to their equipment. They told me the alternator was bad but tests on the weaker end. If i take the car up to autozone where the alternator tested 14.5 volts then read maybe 13.1 would have to be a different problem.

 

There is no “other” section in general…general is general !!…what are parasitic drain type connectors ???…if you are referring to alligator clips you can purchase 4 mm banana jack leads as a kit that has various connectors on them…alligator clips, backprobes etc…yes, you use the diode setting on the DVOM as was illustrated in the video…I would HIGHLY suggest you watch YouTube videos on DVOM use…there are many on there as well as basic electrical 101…you can also purchase an AMP clamp that connects to your DVOM which allows you to measure current draw without having to disconnect the battery leads !!

 

i dont know i found the parasitic drain type of connectors on amazon look like real nice epuiment and includes instructions to do so. To me the instructions read easy.

 

Thanks c5 diag. I tested the other alternator that would kill batteries vs a good ls1 alternator. The bosch 140 amp reman reads a 2000+ reading one end and 507. The good ls1 alternator reads .534 as it should and 0 on one end. So its safe to say the saab bosch reman alternator has a bad diode. I need to check the replacement alternator tomorrow on the car to see if its bad but should be fine. This should help future people test bad alternators or something that would cause a battery draw.

 

It must be an intermittent problem. I just tested the same bosch alternator after testing it earlier with the same results and now tests good as far as bad diodes. The car runs good with new battery just every few months he goes out to start it and wont start or needs jumpstarting. Im assuming that is when the issue or bad alternator takes place causing overnight battery drainage.

 

Hey, Justin. This isn't any help, or harm. A bit off topic. As I recall, you're rescuing a sort of rough C5, correct? Or am I confusing you with another member? Best of luck either way......

 

Yes sir that would be be. The guy sold me a lemon about half a year ago when i had about 10k to spend on a car whether it be a c5 or a 8700$ 2005 black c6 that had a bad 3-4 gear would've had to have been trailered about 149 miles from where i lived. I didn't see the A6 transmission for c6's are about 900$ on ebay and maybe the 05 could be converted to A6 with torque tube. Should have went with the rebuilt title c6 as i bought this c5 with what was advertised as no running problems bought it on the way home 177 miles from laredo had some racket the torque tube was trash and one fan blade was hanging temps were in the 239-241 range as the cars air dam was missing. Told me the car drove normal and requested i meet him up where he was at work to buy the car just inside of laredo. Yes that is me trying to doctor a c5 back up to normal. I read somewhere that the c5s have a "overheat protection that will disable fuel" if it got too hot or is this not all c5 corvettes? I currently have a 91$ kmj balancer, elgin 220/224 cam and waiting on springs to do a cam swap as it has the factory balancer with some bad rubber i noticed after replacing the continental decoupler pulley to quiet down the marbling under the hood. The guy disclosed that the car had a couple of exhaust manifold bolts broken in the head and that was it before purchasing it for 6800$. I figured it could get my 6800$ back worst case but after receiving it torque tube was trash, exhaust manifolds puffed a broken exhaust stud on each side, cracked leaky surge tank, the alignment was way off car would wander and felt like rear cradle was loose, felt like it could 180 anytime just getting out of laredo and the lower radiator support was barely there as missing upper radiator support and hood struts. Found out the heads were fine on the exhaust side bolts but the rear most intake bolt was stripped when trying to torque 5-8ftlbs. Im in it about 10k with the car, repair parts not including torque tube labor and header install or radiator support. I will say it does drive nice across down to the bank and other daily driver type of stuff. i don't know why they made it to where you have to remove the passenger header to access the starter. I do think some or most c5s that havent had the torque tube repair will probably run into the same issues with rubber couplers the vibration isn't really an issue with the solid couplers theyre 100 grams lighter. then factory rubber couplers. One thing my name is justin raney similar to ran e but pronounced rainy and the intake filter position is bad on these cars if there isnt a hood seal present i was driving thru a heavy thunderstorm and quickly turned around to head home as im afraid of water getting thru the filters.

This car with the parasitic drain is my brothers daily driver 2006 saab 9-5 that will kill a new battery every few months runs great 260hp turbo 5 speed auto. He uses it daily for work and most days its fine just sometimes he comes home the next day for work the car doesn't start or at work it'll need a jumpstart. I checked the alternator diode reads 2000 when it should read 0 yesterday midday multipe times and compared to a nearly new ls1 f-body alternator later in the evening it tested okay or 0 similar to the ls1 alternator. My c5 doesn't have a battery draw and the volt gauge i think is slightly off as the underhood fuses with an expensive probe meter read 13.7 and 14.2 on almost all the fuses. I did use a spare 08 saab parts car bosch alternator and bracket that fits the later 140 amp alternators and has a decoupler pulley similar to the c5 auto. I would have gone with a 6 speed but at the time searching for cars my left arm was in bad condition after being in a wreck at 27 feb 2017 in my 01 escort causing my left arm to snap on the steering wheel and whiplash which months later found out my neck was broke, every disc thrown and a 4 pack. After that i started looking for a daily driver ls1 v8 as i had a 95z28 6 speed at 18 and 98 z28 hardtop 6 speed at 19.

 

It'll be hard to track down that kind of issue, but I'd be searching for something that sticks on every now and then. Remove fuses for non-essential stuff and see if it stops.

 

My BCM did that years ago. It got progressively worse until we finally pinpointed it. It was a heck of a drain, sometimes totally draining the battery in 12 hours, or less.......

 

this might help...
Here is a cut and paste from a Bill Curlee post from some time back about common parasitic drains in the C5:

The correct BCM current draw should be 20 Milliamps or less. Most C5 run around 25ma
but I have see some as low as 15 ma.

Leave the engine compartment fuse box for last and start with the passengers compartment
box first. Pull the power seat breakers FIRST! The power seats have a tendancy stay on
and cause this issue.

Also pull the fuses for the Bose system amp.

Examine the car in the dark for lights staying ON.

Once you prove the interior circuits good,,, check the headlight circuits, and then test
the current draw of the alternator.

Look at my electrical stickey. I think I cover this in detail in that post.

There are several COMMON things that cause excessive current draw

-Seat multifunction switch & Lumbar Switch
- Bose Amp relay stuck on
- Alternator didoes bad and drawing current
- Headlight control module bad
- Interior light on (check in the dark)
- Added aftermarket accessory not shutting off

 

Thought I'd add my experience. After I got my 99 coupe home it would drain the battery overnight. Bought an Optima red top. Drained that too. Had to put old battery back on and connect to charger overnight if I wanted to drive it next day. Changed out seats with non powered aftermarket. Pulled related fuses and problem completely went away. Got Optima back to life and haven't had put on charger since, (about three months).
I don't know which seat was drawing juice. As both were powered. But that might be a place to start.