Yesterday after coming out of the movies (saw The Magnificent 7, good flick) I remotely unlocked the car, then sat down. Put the key in the ignition to start her...no dinging, nothing...dead...nada. I checked to make sure the it was properly engaged in P, I mean I had just remotely unlocked it... and tried again...nothing. I looked around at the parlor lights since it was under a minute I had been in it and they were out.
So, to the trunk I go, pull up the cover and check the battery connections. Everything was tight and clean, even took a peek at the relays. I was about to call AAA, when I decided to give her a go one more time. I opened to door and the lights came on, put key in, she dings and she starts.
I'm happy for that, but I'm concerned as to why it did what it did? The connection was flat dead somewhere. I know this because she kept revving a minimum 1100 rpm almost the whole way back to the house (about 5 miles) relearning the ECM, except where I was on the expressway. Everything on the stereo had to be reset and the clock (which is very accurate) was off by 3 minutes for the time I was fiddling with it. My first thought was battery cable, checked it again at the house with tools...real tight, no movement on both terminals. I did an OBD check and voltage, 13.4, no codes. I've driven without issue now for over 24 hrs, she fires right off.
So, I tried to do some searches here to no avail...do you folks have any suggestions for the cause of this?...or a thread that didn't come up from my search I can review?
Thanks y'all in advance.....

 

Batteries these days (past 8 years or so) are straight up crap IMHO. Could be a momentary short in the battery that corrected itself. My last NAPA ( pretty sure they are all mostly Johnson controls now) battery for my XJS, I had to go through 3 to get a good one! Not saying it's your batt but I have zero faith in them anymore.

 

You would be surprised on what micro corrosion can do. In my 22 years in the automotive field, only about a half dozen cars I have come across with this strange behavior. I would take both battery terminals off even though they look clean, go clean them anyways.

I had also one time come across a battery in an XK8 that I ultimately found to have the hold down bar too tight and cut the entire car/electrical system off after driving 45 minutes. One of the lead acid plates in the battery under the positive post expanded enough when the battery heated up and bowed which caused an open circuit like the positive terminal was disconnected while driving. A new battery cured that problem.

I would also consider removing the ground cable from the body and clean that area as well.

 

Thanks for the replies JT and boost....
Oh no I wouldn't be surprised by micro corrosion, that's why I had replaced the positive terminal about 7 yrs ago and inspect it regularly (about every 4-6 months) and use a battery tender when not being used after a week to maintain it and keep corrosion away.
The ground cable is clean under the mount, I checked that also. Also I would expect it to be very warm to hot if it were the ground being it would be trying to draw power without proper ground.
I have definitely not ruled out a bad battery (I think this one is 6-7 yrs old), but to go from good to dead to good is definitely a new experience for me. With Sears going out of business, they may have batteries for 20-40% off, wouldn't hurt to take advantage of that.
Any other battery I've had at least had some residual power and little things like the clock ticked or the parlor lights would be dim. Everything was dead with this.
One other test I did when I got home was to turn the car off and put the lights on. They were bright as they should be, I even put them on high beam and the fog lights.

 

If the ECM was randomly hard-reset then you are highly advised to get a new battery (assuming it is more than a 1-2 years old.)

If the remote keyfob worked but then did not start that actually sounds like the RFID in the security key did not disengage the security system the first time you tried it. Not sure what happened, but if it happens again, try using a second key (in reality, it is far more likely the RFID reader in the steering column would fail than the RFID chip in the key, but gotta start debugging somewhere...)

 

When the battery went on my first XJ it did exactly what yours did, only I had to get a jump start. A 7 year old battery should be replaced anyway, I treat batteries like brake fluid and replace every three years regardless of condition.

 

I appreciate the response, but the only thing the RFID does is release the activation to turn the key. I install these systems for the military, colleges and such. Also, the system was totally dead, no interior lights, no dinging from engaging the key, no trunk release from the fob nor the dash button, I didn't even have emergency flashers.

I'm going to go down and have them put a load on the battery today and see what the results are. I agree with Stu and JT about battery life, even the good ones are limited on lifespan.

 

Sorry it took so long to respond again, but I was called out of town on business and now we're dealing with a little issue called Matthew off the Florida coast. But I did get down and had the battery tested yesterday and the tech said its perfect, everything is spot on, even gave me the print out.
So I went over to my indy and he said it possibly may had been the mega fuse, (...in the trunk by the spare below the fuel tank). But, because its working now, its hard to access if it actually was the issue. So, its probably not a bad idea to simply replace it and err on the side of caution, they are cheap, only around $5-8 and there's 2 to replace. It might be all of a 15 minute job, most of that getting the spare out and back in.
If I find out later its something else (or you have another suggestion) I'll post it.
Thanks again for the ideas and effort in responding....

 

They're dead easy to get to, take out the spare wheel and undo the two nuts holding the cover on. Then you unbolt the fuse.