1987 Jeep Battery Discharging

[MJE49]

I have a 1987 Jeep Cherokee, 4 cyl, 2.5, 198,000 miles. The battery is approx one year old. Recently the battery has been runnig down over the course of a couple of weeks. I had the battery and the alternator tested yesterday and both tested fine. According to the shop that tested the alternator, the voltage regulator is built into the alternator. I ask him what else it might be and he said to disconnect the positive cable, turn off anything that pulls current, and connect the post and the cable with a test light. I did and the bulb did not light up. I have cleaned my battery terminals and cables. Any thoughts on what the problem could be?

Jay

[goldstar]

If your vehicle sits a lot, a small drain will pull the battery down over time. A better check is to hook a volt meter set to 1 amp or less in series with the battery. If there is a draw, start pulling fuses one at a time, until the ammeter drops to near zero. Then check out that circuit. Other things to check are glove box, under hood, or trunk lights which may not go off because of a bad switch but cannot normally be seen in a lit area.

[Lugnut]

Did you perform the test light procedure with the key on, both accessory and run position? To be sure you are doing the procedure correctly, turn your headlights on briefy to verify the test bulb will light up.

[MJE49]

Lugnut, yes the key was off and all lights were off. Since I wasn't positive I was doing it right, I opend the door to check and the light meter came on, I also pulled on the headlights and the light meter came on.

Goldstar, I have a small multimeter and after I checked the light meter I tested with the multimeter. I set the meter to 50 DC and touched the post and the cable the needle actually went the opposite direction. I didn't know what that meant, but since the light meter did not come on I figured there was no current drain.

[hspr]

What kind of test light are you using ? One that uses an LED won't work here, must be the old regular bulb type. Even then a draw that kills a battery in a few weeks might be too faint to show up. For something so subtle you might have to take it to a good electrical shop with an amp clamp. This will precisely determine the amount of the draw and reveal the offending circuit much more easily.

A battery running low after a few weeks is not necessarily unusual. If you read the manual for new cars, they usualy give a limit of about two to three weeks and assume a draw of about 50 milliamps. Your Jeep is not new, I understand, but a certain amount of draw in an sitting vehicle is normal.

The most common draws we find are traced to aftermarkent equipment, stereos, power lock systems, remote starts, etce. If you have any of these, you might try leaving them disconnected. If you can't find the problem, why not just disconnect the battery if the vehicle is going to sit ?

Good luck.

[Lugnut]

Since your test did not indicate a clear and present drain, I would also agree that the battery drain may be normal for the condition of your battery.

Keep in mind that although the battery is one year old, and tested 'good', it is still not a new battery. Battery testers determine your batteries ability to crank the engine. They do not test the capacity for a battery to bear a parasitic drain.

If you do have a drain, it is a very small one since it does not light up the test light. To isolate drains that small, sophisticated automotive digital/computerized meters are attached overnight to capture the precise strength and time of day and length of the drain. These test are usually perfomed when a battery drains over the course of a day or two, ergo, not 2 weeks.

I would be more concerned if the battery were being drained every day or two while being driven each day. A passive solar charger (around $60) may be of interest to you. Or just a new battery.

[MJE49]

hspr, I believe it is a regular bulb. When I opend the car door to test it, the light came on. The car has nothing added.

The test you recommend, is this something that a retail store, such as Autozone, would be able to test?

Thanks for your help.

Jay

[Lugnut]

No, an auto shop with trained techs and with the expensive specialized equipment do those overnight tests. You would have to ask them if they have the equipment to find parasitic drains. Most shops do not.

[goldstar]

If you were on the 50 volt DC range, and the needle tried to peg zero, you had the test leads reversed. If your meter has a range setting such as 1Amp or 500 milliamps, use that range in series with the battery. If you do, DO NOT open the door or turn on lights during the test or you will fry the meter.A very small drain is normal because some power is used to keep the memory in various components.