When I went to leave for work this morning I found my jeep dead. After putting it on a charger for a few minutes, then setting to "boost" I was able to get it started. About a mile from my house though the voltage gauge pegged out. Once or twice in my 10 mile drive to work it dropped back to normal for a few seconds but pegged back to 19V again. When I got to work and shut it off, it was immediately dead when trying to restart. I was able to get it started again using a charger.

My first thought goes to either alternator or bad/loose connections. Any other thoughts? The battery is about two years old (and I really hope this "issue" hasn't killed it.

 

Any of the following....damaged or corroded battery wires, dirty or loose wire connections, a failing battery or a dying alternator.

 

What year/engine? There are significant differences in the charging system through the years.

Job #1 is to figure out why your battery was dead. Have it LOAD TESTED at any parts store for free. Gotta make sure that is good early in this troubleshooting process.

And if the battery checks out, verify charging voltage at the battery with a meter to confirm what you are seeing on your voltage gauge.

 

D'OH, sorry... it's an '01 4.0L.

After closer inspection, my cables can definitely use replacement. Whether that's the problem or not, I'm not sure. I'm going to take the battery to the parts store when I go to get cables. While I'm not fond of throwing money at things, it seems like it would be foolish of me to not pick up a new alternator as well considering the one in the truck is the original with 160K on it.

It's just really odd that once it's running it operates fine (with the obvious exception of the gauge).

 

Hey guys- had this same issue with my 01 xj, and I read from various sources that it is most likely a bad connection. I went to autozone, bought some terminal cleaner and a wire brush and went to town on my battery connections. I also tightened all the wires and grounds connected to the battery- and (fingers crossed) haven't experienced the issue since.
I assume what happened is that the connection was poor, and the alternator/voltage regulator read that as a weak battery, and kicked up the voltage feed to charge.

 

I had a similar problem just 2 nights ago. I was driving home at night and suddenly the "check gauge" light came on, and the voltage gauge was pegged at 19 volts. I was tempted to pull over and turn off the car and restart, but gladly I didn't. As soon as I pulled into my parking spot at home, I turned it off and tried to restart. It made a few clicking sounds from the starter solonoid and all lights went dead. The lights eventually came back on after 30 sec or so. I attempted restart again, but the results were same. A few clicks of solonoid, all power lost for 30 seconds or so.

Today I got a multimeter and checked the battery at post. It read 12.78 volts. so it's not the battery. I started continuity and resistance (ohm) test on all battery cables and different connection points. All came out ok, except a little resistance in the main Ground wire from battery to Fender.

I took the bolt off of the grounding wire at the fender. It looked fine. No corrosion, except it looked ever so slightly white.

I sandpapered the wire end, connected tightly, then attempted restart.

At first, it was just clicking the solenoid. But it was a few more clicks and the lights/power didn't go out for 30 sec or so. It came back almost immediately.

I waited about 1 min, then tried to restart again. This time it cranked over and started.

After a brief warmup, I took it back out for a drive. However, a few 100 yards out, the Jeep died on me. The idle became so low, around 250rpm or so.

It ran fine except at a complete stop. The idle speed got so low that it cut out on me a few times.

I thought it could be low gas (fuel gauge light was on). So I filled up with gas. But the low idle problem persisted.

When I came back home, I disconnected the ground wire from the battery in an attempt to reset the computer.

After a few minutes, I reconnected the ground wire to battery and restarted the jeep. The idle speed came back to normal.

I turned the ignition on and off several times. The Jeep works now perfectly.

Just to add, before the electrical problem 2 nights ago, I noticed that my voltage gauge was reading 14 to 15 volts. I was actually glad that the charging system was working so well. However, that was a sign of bad things to come. Now my voltage gauge reads just below 14, cranks up on first try, and idles ~750rpm.

Once I get some time I plan on upgrading all the battery wires, and install multiple grounding points with heavy gauge wires.