Lost all power - like the battery was removed

[Cottontail]

2004 WJ 4x4 4.0L

Wife drove it a couple times this morning. Started fine every time. Got to an appointment and shut it off.

• Went to hit the power lock button on the door panel and it wouldn't work.
• Tried to start it up and it was completely dead
• Called me to help
• 40 minutes later I show up and turn the key and it fires right up
• I notice the clock was reading 12:20 when I started it - meaning, it must have been without power for at least 20 minutes before power was restored
• I drove it home and made a few stops. Never acted funny or tried to stall and started up fine each time I completed a errand.

Not completely sure where to start. I did just have a major overhaul of the cooling system - thermostat, water pump, radiator, upper rad hose. Doubt that has anything to do with it, but for good measure I'll mention it.

Mileage is currently about 206xxx. Had a new alternator at 171884 (May 2014) and a new battery at 176236 (August 2014).

 

[iluv83vettes]

Check your grounds. When I first got my new XJ, I went on a longer trip and stopped for lunch and when I tried to start it back up, it was completely dead. The ground for the battery was completely corroded so I stripped back the wire some and reattached it. Next step was make an order with Jon Kelly. I really wish he was still doing cables.

 

[Cottontail]

Everything looked good. No real "warning lights" to speak of. I did find that the negative battery cable was a little loose on the battery, so I tightened that back up. I also cleaned up the connections on the block and the starter.

So far, no issues. Of course, now that this has been written, it will stop working later today.

 

[old_man]

I have seen an intermittent open within the battery. A cheap simple check is to just try and short across the battery terminals for a split second with a pair of pliers or a short piece of wire. If it sparks, the battery is good and you need to start working out from there.

 

[iluv83vettes]

If your negative cable was loose I bet that was it.