New battery dead in 3 weeks?

[AVR2]

Changed out the old battery 3 weeks ago. My wife just called me to tell me that she went to start the Jeep just now and it's acting just like it's dead again. Keyless entry worked to unlock the doors, but absolutely no response when she turned the key.

I'll get my voltmeter onto it when I get home, but I can't help thinking that it's probably going to be the charging system. Unless I've just been VERY unlucky and bought a faulty unit, a brand-new battery from a reputable brand (AC Delco) shouldn't do that, right?

 

[LibertyTC]

The charging system in the KJ seems to be very reliable.
It is not that uncommon to have any new battery need 2nd replacement.
They will give ya another one if faulty.
Get your volt meter on battery, before and after you start it.
Take it back to place you bought battery with receipt, and ask if they can diagnose charging system for you as well. Chances are it is just the battery.
You could have a drain down as well, but start by taking that battery back.
I charge my batteries while at home and keep em topped up.
The waterproof C-Tek charger is awesome for that purpose.
http://www.jeepkj.com/forum/showthread.php?t=47021

 

[LibertyFever]

So just why did you replace the battery three weeks ago? Was it mysteriously failing too?
Maybe you have a parasitic drain on the battery or maybe a bad alternator. Both can be diagnosed.

 

[AVR2]

I replaced the battery because it was dead and had lasted about 14 months (which is about as much as you can expect from a battery where I live - if you get 18 months out of one, no matter what make of car, you're doing well).

I've just got the voltmeter onto it and it's producing 12V and the little indicator eye is showing green, so I guess I can rule out a bad battery?

Despite that, it's acting exactly like it does when the battery is dead. Keyless entry is now not working. When I first opened the driver's door, the interior lights and the odometer display didn't come on. I popped the hood, closed the door, checked the battery - and then when I opened the door after that, the lights and odometer *did* come on. I put the key in and got the "key in ignition with door open"chime. Then I turned the key, the lights and odo went out and the engine didn't even try to turn over - no clicking relays, nothing. Totally dead.

I'm going to try disconnecting the battery cables and cleaning them just to see if it makes any difference (you never know). Other than that, are there any likely culprits? Any fuses that may have blown? It's a 2005 KJ Limited.

 

[LibertyTC]

When Charged after sitting all night a new battery should read about 12.7 to 12.9+ volts.
When the KJ is running you should have a reading of about 14.7 volts. What is your output voltage?
Somethings not working right.
You can greatly extend battery life by having your battery trickle charging like with a C-Tek charger...
Got a charger there..??

 

[AVR2]

Problem is solved

Cleaning and re-tightening the battery clamps fixed it. I thought I'd cleaned them well enough 3 weeks ago because the Jeep was running fine until this morning, but obviously not.

Just FWIW, before I disconnected them I realised I'd only measured the battery voltage directly from the posts, so I measured it from various points on the clamps and it still read 12V. At that point I figured that cleaning them probably wouldn't make much difference but I did it anyway. Reconnected, and this time there was a relay click when I turned the key, but that was all.

I disconnected again and had one more go at cleaning the clamps, and I also noticed that while the positive clamp slipped easily over its post, the negative one didn't slide all the way down to the bottom, so I persuaded it with the end of my Maglite. Tried the key again, and bingo Got the voltmeter back onto the battery and it was reading 14V, so from what I understand, that means the charging system is working OK.

I have to say, in my experience the KJ seems to be very sensitive as to how its battery clamps are connected, much more sensitive than my ZJ, or indeed any other car I've owned. I had a similar experience with my KJ playing dead after I reconnected the negative cable following some work I did last year. I had to clean the clamp thoroughly before it would start.

 

[LibertyTC]

As mentioned in my how to article, yup they have to be tight & clean, otherwise you may have a very poor connection and power supply.
Use a wire brush or emory cloth sandpaper to clean inside the terminals so they sparkle.
Then coat them in Petolium jelly (vaseline) to keep it all in top shape.
If ever you get a science project, ie; green & white powder happening, use baking soda & water to remove build ups. This kinda stuff is not acceptable for optimum connections and will eventually destroy the cables.

 

[moparman]

Hopefully "persuading" the battery terminal with a maglite didn't crack the post or case.

 

[J-Thompson]

Just FYI
volts means very little on a car battery
they are more about current or AMPS
I have seen in several cases not just in cars but also in SLA's where they will read 12V
on a standard VOM but loaded down and they tank to under 10 volts
easy test is check for volts under no load
then check with the head lights on
a bad battery will tank a good battery will hold 11.5 or so
*check should be with the engine OFF