For months now I have occasionally found the battery dead after not driving for several days. Sometimes down to 3-4 volts. I have in that time replaced the alternator once and battery several times. The alternator failed completely and was delivering 0 volts. The batteries, I believe, failed from being severely discharged. It’s possible I have left something on from time to time and also possible that I’ve had more than one dud battery in a row but I fear there is still an undiagnosed issue.
Several times I have checked the current at the battery with the engine off. I’m not 100% certain how to read amps on my multimeter but I measured with the selector knob turned to 20m, Red lead in the 10A socket, black lead in the COM socket and the leads between the battery and the disconnected cable. It read .1 for about 30 seconds and then 0. I took this to mean < 1 amp while the electronics initialized and then 0 amps. I.e., no parasitic current while the engine was off.
When the engine is running I read about 14.7 volts between the battery terminals.
Today, after not driving the truck for about 5 days, it started a little slow. I shut it down and measured 11.6-11.7 volts on the battery so I drove around a bit to charge it.
The battery is 2-3 weeks old and this one has not been severely discharged. In the last week temperatures have ranged between 0C and -26C if that matters.
Am I still suffering a problem I need to fix? Is a battery down to just under 12 volts after almost a week a problem or has my past experience made me hypersensitive?
I have a few tools and time here and there this weekend to try diagnostics you suggest.
With the engine running, your reading of 14.7vdc at the battery terminals is the voltage being supplied by the alternator. That’s not the battery voltage, but the alternator’s voltage you’re reading.
Your problem may be an old, weak battery (even if you just bought it) that simply needs replacement. Have a local garage check the battery’s condition with a battery load tester. A battery not under load may show 12vdc, but the voltage may drop under load.
Another possibilty is that you may have a parasitic votage drain. You can check that with an ampmeter (a voltmeter can show the same thing if you have the time to wait for a slooooow reduction in voltage).
Monitor the battery amperage, and begin pulling fuses one at a time. Replace each fuse before pulling the next one. If you notice that one (or more?) circuits are drawing too many amps, check/disconnect the electrical equipment on that circuit, one at a time. Also inspect the circuit’s wiring. Replace/repair the obvious (shorts, grounds, burn marks, burnt smells). Hope this helps. Good luck.
GM vehicles have this … odd feature of leaving the accessory (cig lighter) ports energized all the time instead of switched off through the ignition like most cars. Be sure you’re not leaving things plugged in and powered on such as dash cams or phone chargers. Also be sure there’s not some piece of crud or something intermittently shorting them out.
Though I doubt this would be an issue on a '97 S10, some cars have different levels of hibernation so to speak. For example there might be some security system that doesn’t kick on until a few minutes after being armed. So what you might try is shut the car off, wait 10 minutes, pull the NEGATIVE battery cable and then measure current (amps) between the negative battery pole and the disconnected cable. Also leave the ammeter in place for awhile (with the negative still running through it) and check on it periodically over a few hours. If you see it go over 30ish MA then you have a problem somewhere. Start isolating it by pulling fuses until it goes down.
It’s also possible that you have a bad diode in the alternator which can drain a battery.
I have a '92 Dodge Dakota with a similar issue–some weird ground side fault that has proven impossible for my mechanic to find. I mean, there just isn’t enough wiring in one of these things for it to have much to go wrong. We thought we had it licked when it was discovered that the horn assembly was pulling current while the vehicle was shut off, and there’s a known fault in Dodges of that era that one of the tail lights can do the same thing but even after pulling the horn relay fuse out it still goes flat if I don’t drive it every couple days. So I spent like five bucks on a terminal isolator and when I park it I crank the knob around so there’s no connection and therefore no leak. Sure, I have to reset the stereo and the clock every time I drive it but it sure beats it killing batteries–it managed to murder four or five by actually killing off cells in the battery and there ain’t no coming back from that. I was just pulling the negative terminal off but my mechanic wagged his finger at me for driving around with the terminal that loose so the isolator is the better solution overall. Old vehicles and random ass electrical issues, it’s like peanut butter and jelly!
I had an old Sonoma that killed a battery before I figured out the problem. The battery wasn’t held down and would bounce up and arc off the hood while driving over bumps. It doesn’t seem like your problem but I’m throwing it out there because it was a hard one to track down.
If your meter selector switch is like this, then the 20m (twenty milliamps/20mA) setting and the 10A socket don’t work together.
To avoid blowing a meter fuse if there is a significant drain, start with the 10A setting and the 10A socket. If it reads less than .2 amps (=200mA), then it’s safe to change to a milliamp setting. Set it at 200mA (20 is too low for many vehicles’ normal parasitic drain) and use the VΩmA socket. I like to see 40mA or less. If it’s higher wait for all the modules to “go to sleep.” This can take from two minutes to two hours; be sure any automatic shutoff is disabled.
Oh I forgot to mention, when you go to disconnect the negative terminal, you’ll want the ammeter clipped on to both the cable and battery post PRIOR to unhooking the cable. That way you maintain the circuit and don’t risk resetting something and invalidating the test.
Now we’re getting somewhere. I was indeed reading the amperage incorrectly. On the 10A scale I get 3.76 Amps for several seconds then it goes down to .16 Amp. When I pulled the courtesy light fuse, it went to 0. It’s too cold to spend much time outside today so I’m leaving the fuse out until it warms up and then I will try to trouble shoot the courtesy light circuit. This will be problematic for a klutz like me.
I assume .16 Amp is not enough to kill the battery overnight but is enough to cause problems over several days?
Thanks to all especially Gary T who put me on the right track.
Correct, 0.16 Amps is 160 milliamps. The GM spec for acceptable parasitic drain (for alarm and passive entry systems) is 30 milliamps. 160 will drain a healthy battery in ~a week give or take a couple days.
Dirt (Surface discharge) is a common problem when there are several days between use but this doesn’t sound like your issue here.
Do you have a under the hood light?
Faulty trunk lights and engine compartment lights are good for killing a battery in just a few days and hard to find. They are suppose to turn off when the lid is down but don’t always do what they are suppose to.
I have had 2 cars that had this problem and just a couple years ago one of my grandsons had the same problem, found that one right away
I did some poking around on Sunday and didn’t find the problem. Thanks for reminding me of the under hood light. I think I will have to do some checking at night because otherwise I can’t even find all the lights.
Not sure how to test for something drawing a current without turning something on. I saw that some of the underdash lights have a voltage at the connections when the light is off. Is the switch on the ground side of the light? Can this voltage get back to the battery through some short? How would I find that?
One thing that makes me anxious about this truck is that the interior lights stay on for a little while after the door closes. I guess if they stay on, the current would be 3-4 amps. Probably isn’t the problem–just makes me think more than I want to.
Anyway, I won’t be losing anymore batteries while the fuse is out so that helps me sleep better.
I am not sure how every switch operates. some are just inputs to the PLC or computer especially the ones on delays.
On the 1st car that had this issue it had been in the body shop for deer collision repair and the under hood light/switch was installed upside down and after a couple battery replacements i saw no frost on the hood in a neat small circle.
As for testing Gary T is much more qualified as are many others, however i do use a totally Redneck method of troubleshooting! i when possible dis-connect and then watch for a spark when i reconnect. a dead circuit will not spark AND for those nuisance check engine lights a 1 inch piece of electricians tape and problem solved!
So use my advice at your own risk
So far we know that you have a 1997 Chevy S-10, and when you pull the “courtesy light fuse” the amp draw drops to zero.
It would be helpful if you told us which engine is in the S-10, whether it’s an auto or manual trans (there might be a different wiring schmatic), and if it’s a Canadian, or U.S. manufacture. It would also be useful if you supplied the number of the courtesy light fuse.
Meanwhile, disconnect each electrical component, one at a time, along the courtesy light fuse circuit. Replace the fuse, and check your amp draw. One thing to remember is that while you’re poking around, moving wires, and jiggling components, your trouble might go away. It happens. Bad connections are made good, relays become unstuck.
