Mysterious power drain on my battery

I have a 2000 Chevy Cavalier with 10,000 miles. We recently started having difficulty starting the car, so we took it to the shop. The mechanic did some tests and found a voltage leak (170 miliamps) that continued to exist after all of the fuses had been removed, and the alternator and starter were disconnected. He said a voltage leak could be tolerated if is was significantly lower, but this leak drains the battery. What could possibly cause the leak? Someone suggested that installing a kill switch could solve the power drain. Any thoughts?

Take it to an auto electric specialist.

I agree, looks like it’s time for a pro.

Looks like your mechanic missed a fuse or two. He needs the “power distribution” wiring diagrams for a 2000 Cavalier.

Start buy pulling maxi fuses & narrow it down from there.

ALL the fuses removed? In the dash fuse panel AND in the box under the hood?

If it fact all the fuses were removed, even the ignition would be dead.

Kill switches disconnect the ignition from the battery.

If the mechanic found a voltage leak, why didn’t he trace it to the fault?

How old is the battery?

I agree with the auto electric specialist and I have the name of one in my area. I was looking for the cheap way out. As far as the fuses go, yes ALL of the fuses were removed, including under the dash and the hood. As far as the voltage leak goes, his equipment said the leak was at the cluster and those were the first fuses he pulled, but the leak was still there. That was when he started to continue to pull fuses. BTW, the battery is brand new. We got it once the problem started in May.

I guess the real question is if there is anything in a car that is not fused. And, if so, what would it be? Also, there is nothing after market on this car. It is a complete bare bones model without power windows or seats. You might say, el cheapo version.

With only 10,000 miles, the car hasn’t been run long enough to wear a wire thin so as to cause a fault (I wouldn’t think anyway).

We recently started having difficulty starting the car, so we took it to the shop.

Explain your driving habits with this car. For example, how long does it sit between uses and what kind of driving do you use it for? This will help to determine if a 170 ma draw is your only problem. If it sits a week between uses and you only drive it 5 miles to get groceries, that would be helpful to know…

That may be normal. If the vehicle has a power save module, that extra current may be operating the relay for 10 minutes before it drops down to 20mA. This should be very easy to track down by someone who knows what they are doing.

Driving Habits: The car was driven only 7400 miles in 7 years, all of the miles were put on in the summer months. It sat in a garage over every winter with a trickle charger on the battery. I bought it from my Dad in January, and we have put 3000 miles on it over 6.5 months. Most trips (by my 16 year old son) are for periods of 30 minutes or more. Who knows where he goes, but all of the miles except a few are his. It rarely sits more than a day or two between runs.

What is a power save module? I think I need to go to the auto electric expert.

The 20 minute power retention system isn’t enough on its own to kill the battery, providing the charging system is operating correctly.

I have the system in my '00 Olds and have never had a dead battery. Thanks to the battery saver (opt) GM installs.

Any possibility of rodent damage to wiring? I was thinking with that low of mileage must have been parked alot.

That seems like awfully low miles for an 8yr old car… Maybe a bad capacitor somewhere, or the airbag system. I agree with seeing an auto-electric expert, also check for factory recalls on your model. My girlfriend had a cavalier and all we ever did was PUSH it around. Last American car we ever will own. The $tealership MIGHT have a clue, but probabally just say “we can’t diagnose it” like our car.

The drain is not excessive based on your usage. At 170ma, even the most puny auto battery will last around 20 days if in top condition and fully charged. Your usage pattern should be able to replace the charge lost during sitting and starting the engine. So, although you have this drain, I don’t believe it is your problem.

Batteries can lose capacity over time. Although it has the correct terminal voltage, it may not be capable of retaining and delivering a full charge. An analogy would be a pail of water. As the battery sulfates, it is like adding sand to the pail. The level of water remains at the top but the volume of water is diminished. Although not always definitive, a battery load test can help to identify whether or not the battery has been compromised.

The other thing to check is to insure that a full charge is being output by the alternator and replenishing the battery charge. A slow death spiral can result from a marginal alternator output or bad connections between the battery, alternator and any controls/indicators in the path. Check the charging voltage right on the battery terminals, not the connectors. Make sure that the wiring is intact and not presenting a limit on the current flow due to corrosion.

Sure. There are places which are not fused: the alternator and the starter. The battery drain can be from things that come on, or stay on, after the car is parked. One item, is the radiator cooling fan will be running when you park the car. You think, “It will stop in a few minuets.” What if it doesn’t; or, it does, but comes on again, later?
Visit your car (don’t wake it!) from time to time, after you have parked it. Look, listen, and report any lights, or other sounds you hear. If the radiator cooling fan runs when it shouldn’t, it could be because of a fan relay, or, the engine coolant temperature switch (or, sensor) is turning it on.

Thanks for all of your help. It is greatly appreciated and has provided a novice with incredible insight. After all of the posts and giving it thought, we are going to go to the auto electric expert and see what they say. Once it is fixed, I will post the final diagnosis / solution for everyone.

Thanks again.

Bill, find the source of the battery drain?


170mA is not all that much of a drain. Is the top of the battery good and clean? If there is any electrolyte or other conductive moisture present from the alternator possibly over–charging,etc…, the battery may be discharging between the posts, across the top-outer case. It’s hard to say without seeing it, but it’s not out of the question.