I had my jeep xj (2000 4.0 4wd classic) sit for about 3 months while I was at school, it needed a jump start to get it running that batter was completely dead and wouldn’t hold charge. I got a new one from Walmart (an ever start 34) put that one in and drove it for about a day. All was fine until I had it sit for about 2 days, I went to start it and it was completely dead, only reading about 2 volts on a multimeter. I thought this was a bad battery which was confirmed by Walmart when they charged and tested it they called me back saying the battery was bad and I got a new one for free. Now the new one I have it ran fine for a day, sat over night and now the jeeps dead again only reading .2 volts. What could be causing this? I thought it was a cheap Walmart battery at first but now I’m thinking it’s more jeep electronics related.
I did replace the alternator about 2 years ago.

I jump stated it and it went up to 13.5 after I went and drove it high rpm try to charger the batter a little it still sits at around 12-13.5 does this sound like alternator?

 

Perhaps you're having a pasasitic draw?

 

Perhaps yes. Where and what would drain it till dead through? I am getting the alternator tested right now

 

I had the alternator tested and it passed. I charged the batter up to around 12.3 and then I pulled the battery and it would barley go down by about .01 every few seconds.
does this sound like a bad battery?

 

It's very possible you got a string of bad batteries. Do you check the dates on the battery before they are installed? Some places have batteries that sit and sit and sit before someone buys one of them. That's why it's possible to get a "brand new" bad battery. If you don't already have one, buy a battery maintainer if the Jeep sits any period of time. They are only like $20-$30. Well worth the cost. Not related but does your battery have a hold down bracket? How do your cables look?​​​​​​​

 

My tie towns and cables are in good condition, I did the big cable swap a while back. I do have a battery tender, I just don’t see how it will be find driving and then about a day later the battery is completely dead. I’m going to test this battery and then swap it out tomorrow for a duralast. I’m done with the Walmart batteries

 

You need to do a parasitic draw test and see what's running the battery down. It could be something staying on, like interior lights (the glove box is common), a bad diode in the alternator, or something else.

 

The battery tested good. I plugged it in and now it’s holding a charge. I tried to do the test with my multimeter but I’m not sure if it goes up to a high enough amperage to read anything.

 

The meter really doesn't need to read much amperage, under 5-amps. Do the test with the doors shut and key off. You'll probably see a few amps at first when you first connect it in series, but should drop down to 25-40 milliamps unless something is continuing to draw current. Killing the battery in a few days, you're looking for probably a 1-amp draw with the ignition off.

 

When the battery dies in your XJ, what are the symptoms? Does it try to crank over or simply do nothing when trying to start it? There are other things that can fall into this same category. The CPS (Crankshaft Position Sensor) and NSS (Neutral Safety Switch) come to mind. Just a thought to go along with testing for parasitic draw and the voltage/battery load testing.

 

A standard test light costs a few $ is to test for parasitic draw (and many other electrical faults)

It should not glow brightly when connected between battery + terminal and disconnected battery + cable

If it does, 100% for sure you have parasitic draw

 

Just bear in mind that there are a few items that always draw power even with the key off (and out). If you have keyless entry (or an alarm) it's always on. Also your radio draws power for the station memory and the clock. Granted, it's a small amount.

If you suspect a larger than necessary draw, you can start pulling fuses (one at a time) until the amps drop like described in the video.

 

I'm going to tag on to this instead of opening a new thread.

I am having some battery issues also. I have had my XJ since last March and other than driving it home from where I bought it, it hasn't been out much. I have been rebuilding it so the battery sits for months at a time. I did buy a trickle charger and at times I have that on it. The most recent is I hooked it up after it was sitting with the positive cable disconnected for about 2 months and let it get a full charge.

Today after installing my exhaust manifold, intake manifold, new fuel injectors plus everything related to that job gone over I thought I'd "hit the key" once and make sure it still cranks. I don't have the rest of my exhaust hooked up yet so I didn't want to actually start it.

I just got the requisite "click, click, click" sound. I put a meter on the battery and it indicated 12.6V.

This battery has gone dead on me a few times. I don't know how old it is as there are nothing on the battery that provides that info. I just know it's a marine Optimum battery.

Should I just replace it at this point? I put the Big7 battery cable kit on it and I have had it running/starting before but I think I have had to jump start it as much as I have been able to jump in and turn the key.

I'm not sure where to look beyond the battery. Oh, and would an always on USB charge port drain enough to kill the battery over time?

 

If I leave the USB charger plugged into my MJ, it'll kill the battery over a week or two.

 

I got one of these last year and these would work fine to test if you current battery is any good?