I purchased an old, used 1998 Jeep laredo last year, August I think. I have been having an issue with the battery I think. If I dont use the car for a couple of days, the car will not start and the battery will be empty. I checked and the battery diagnostic is that the battery is a good battery and the alternator is also good. I checked in 3 different auto zones and one walmart, all of them came back with the same result. Any idea where else I need to look? I already made sure the cables were rust free and tight. I don't know where else to look to solve the problem. I like the old Jeep and I would like to keep it, but if I can't figure this issue out, then I guess I will sell it to someone that knows how to solve that problem. Any ideas will be appreciated. Thank you.

Had the same problem with an older Toyota. Check your fuses to see if one of them is shorted. Mine was the fuse to the horn. Pulled the fuse, no more problem. Never tried to trace the short.

Buddy of mine had the same problem, I think he tracked it down to the BCM (body control module) but he used an OHM meter and worked on the fuse block in the engine compartment.

If the battery is OK after charging and the alternator is charging, it has a parasitic drain somewhere. Start with the easiest things first. Interior ("dome" or map) lights being on through malfunction or being left on and glove box or under-hood illumination lights not going off are common problems. If these are OK, then it gets more complicated. You have to disconnect a battery terminal and then put an ammeter in series between the cable and the battery. With everything shut down there should be no more than about 50 ma (milliamps) showing on the ammeter. If there is, you start disconnecting fuses until the drain goes away. Whatever is on the circuit fed by the fuse is causing your drain. With the fuse box(es) under the hood, every time you open the door to pull a fuse you have to wait for everything to power down again. Also disconnect the large alternator output terminal; sometimes faulty diodes in the alternator can cause a drain. Have fun.

Do an ignition-off draw test. This is the amount of amps your vehicle draws when everything is on the off position. Every vehicle will pull a certain amount of current even when off. I have a 2003 Grand Cherokee and the spec for my ignition off test is 35 milliamps. A few years ago I found my battery would die if I let it sit for a few days; while running the alternator was charging fine but if I didn't run it a few days later it would be dead. Before I replaced the battery I did a draw test and found I was only pulling 32 milliamps, within spec. So I replaced the battery. No more issues.

If you find you are pulling more current than specified remove your fuses one by one and see if your meter drops; if it does that is the circuit that is causing the issue.

(ETA What that guy just said lol)

Is there any add-on electrical equipment or other tampering? A couple of things that like to cause drains are alarms or anti-theft devices and radios that are wired hot all the time and have to be turned off manually.

quote:

Originally posted by egregore:
Is there any add-on electrical equipment or other tampering? A couple of things that like to cause drains are alarms or anti-theft devices and radios that are wired hot all the time and have to be turned off manually.

NOPE! No add-ons whatsoever. The battery is brand new. The alternator I was told it was replaced within the past year, and it looks new. I have checked inside lights, headlights, made sure radio is turned off. Yet, it dies if the vehicle is not used often. Today I used it, drove it around town all day and did not have any issues. I just parked it and disconnected the battery so it will not die next time I want to drive it.

Remove the negative cable from the battery, hook a test light to the negative on the battery and to the negative battery cable you just removed. Now the light will almost certainly be bright (make sure the battery has a charge before doing this). Now start yanking fuses, 1 by one and see if the light goes out, if so you know which fuse the short is on, now look in the owners manual or online and see what circuit that is to and start looking at the items on that circuit.

Make sure to check the ground wires.

Use a multimeter to narrow the circuit down in the fuse block. Like so.

It was the brake light switch on my Frontier.