slayer2103

I am trying to diagnose a battery issue that I have been having in the cold weather this year. Any suggestions on where to start would be helpful. I've fixed a lot of things on the jeep, but I'm not even sure where to start with this one.
Firstly, if I test the battery at advanced auto or wherever, they say its fine. Here are examples of the issue i'm having.
The first time I had an issue was when it was first cold out. I started the jeep, turned on the heat, and put it in reverse. I heard the check engine light turn on, and the battery died. I did not warm up the jeep in this scenario.
After that I was more careful. Here is what typically happens. I turn on the vehicle. I turn on the heat and let it sit idle. Sometimes in this situation sitting idle, the battery indicator will go down to about 1/4, between 9 and 14. The jeep will sit there idle at that battery level for a very long time, I've sat 15min and it will still be at that level, the fan for the heat is also not going full blast. If I give it some gas, the indicator will increase, but not all the time. Having the lights on during this situation results in the battery indicator never going to its correct position.
When I turn the vehicle on and do not wait 15min but try to drive, the car will sometimes drop to the very bottom of the indicator when I initially start to get moving, weather this is going in reverse or pulling out in drive. Giving it gas usually results in the indicator being at the right level and the fan running at the right level. I usually have to drive until the car is fully warmed up for this to stop, until then the indicator goes to 1/4 anytime I do not have my foot on the gas. If i turn the heat/fan off while driving it is fine, which I usually do at stop lights so it won't stall.
Any suggestions on where to start? This issue seems to effect my lights too, they dim when the battery indicator drops. Going in reverse most often seems to drop the indicator the most too, though I parallel park, so it might just be that I'm going in reverse first to pull out more often.
Thanks in advance.
ps. I have a multimeter, but i'm not really familiar with electronics in the car or where to start testing, or how for that matter.

jordan96xj

The system voltage is dropping when under load, and it is dropping more in reverse because the reverse lamps are coming on in addition to everything else.

This will almost certainly relate to bad/corroded connections or cables under the hood, a failing alternator or one that is not being turned properly because of a loose belt, or a battery that is failing.

Start with cleaning up and all of the connections on the battery and alternator.

tiger02

I had this issue a few winters back as it gets cold and wet here in the PNW. Turned out to be the belt slipping on the alternator. Lights would be dim and voltage gauge reading low. I could see the alternator kick in after a few minutes of driving. Replaced the belt making sure it was tight.

As Jordan96XJ says above loose connection can also be your problem. After a no start last month I've changed all my power cables out for 2 and 4 AWG welding cable to include the grounds. Starts a little faster now plus peace of mind with a more durable set up over the stock 6 AWG wiring.

slayer2103

thanks for the responses.
I actually replaced the battery cables in the summer and when it first died I checked all of those and the connection to the alternator, I don't see any issues there.
The belt might actually be the answer. The car is very sluggish until its warmed up for 10 or so minutes, after that there are never issues. I'm not sure I ever changed the belt in the 10 years I've had this, so that's definitely a possible cause, and maybe the quickest for me to try first.
Are the belts on these hard to change, i've only done it on vehicles where it was a real pain.

Ralph77

Piece of cake. Pretty sure it is 15mm all around. Crack the bolt on the pulley. Just crack it. Then you will see the adjuster to the left of the power steering pump. Couple things. I used to own a '96 XJ. The "yeah that looks about right" method worked just fine. My '00 seems to be more finicky when it comes to belt tension. I suggest you invest in a Kritit II gauge. When I did mine with the "yeah that looks about right" method I checked with the gauge. I was 40 lbs to low. Also buy a good belt. With my '96 the $10 belt was just fine. Not so much with the '00. Gates or a Napa one, which is a rebranded Gates, works for me. Also the pulley you just crack the bolt on make sure you give it a quick spin to make sure the bearing is alright. Do the same with all the other pulleys. Belt tension is:
New Belt: 180-200 lbs
Used Belt: 140-160 lbs

slayer2103

Would it make sense to check the tension on the current one first? I do remember now my dad putting a new belt on a year or 2 back when we were fixing something else. I doubt he did anything but eye ball it. Only thinking this since it's about 20 degrees out and less time outside is a plus.

Ralph77

Of course.

slayer2103

And I would use the "used" tensions you listed above? No where locally seems to have a guage so it looks like I'll have to order one and wait til next week. Thanks for the responses.

Ralph77

Yes on the used tension. Check with your Napa.

https://www.napaonline.com/en/p/NBGKR2

If it is before 5-530 where you are they might be able to get one from their warehouse on the overnight so you could have it tomorrow. That is when the cut off for the overnight is. Cost a little more there but Napa is having a promotion tomorrow. If your local store is participating and since it looks like it is a regular priced item and if you pay for it before 9AM tomorrow you can save 30%. Not really sure if ordering it today but paying for it tomorrow will qualify. I know at my store we would get it and let you pay for it when you pick it up. Even if we don't know you.