Dead or Sleeping?
 

My 2007 XKR has been running perfectly since the engine replacement last summer. Until yesterday. I went to start it, it turned over slowly and nothing. Next try there weren't any lights, and I thought dead battery. I tried my quick jump Suaoki, when I attached it to the battery the panel lights came on momentarily, there was a click and then dead. I then successfully jump started the car from my wife's car using the approved procedure and the car seemed fine. I attached my OBDC and found the charging rate at 14.6 amps, which dropped to 13.8 as I made my way to my friendly Autozone. The battery load tested fine and showed almost a full charge. The engine restarted fine, came home, shut it off and it restarted okay. Came out this morning and the car is stone dead or sleeping soundly. The battery cables were clean but I cleaned and reattached them. Still dead. Put my new 8 amp charger on and within 5 minutes the charger switched to maintenance/trickle mode. No lights come on, there is no sign of life. If it was a relay the car wouldn't have restarted yesterday. Anyone have suggestions for bringing the car back to life?

How old is your battery? Do you drive your XKR daily? Do you use a CTEK or other good quality brand battery maintainer? Do you lock the car when it's parked in your garage? Do you leave the SmartKey in the car?

I suspect the battery isn't holding a charge, notwithstanding the Autozone test. Just a guess. Your answers to my questions will be helpful.

I remain perplexed. I jumped from my wife's car and lights came on, engine started. Let it run a few minutes, turned off and it started again on its own. If it were a relay it would work or not - like a circuit breaker. Insufficient voltage from the battery? Security system reset? Leprechauns? I don't have confidence that I'm not going to get stranded. This is my daily driver. Help?

No help from me if you don't answer my questions.

Stuart, this is my daily driver. I don't use a maintainer as I'm driving 50 miles round trip 5 days a week and haven't had issues til now. I don't usually lock the car and the SmartKey goes with me. I have it back on the charger now and can check voltage with my multimeter. With the engine running just now it was charging at 14.3 volts. I would have thought the load test on top of checking charging voltage would let me know if the battery weren't taking a charge, but the battery seems to be the most likely culprit since I'm able to jump start the car. Thoughts?

and sorry - I didn't see your first post til I just came back in. I appreciate your help.

Next time it doesn't start check the battery voltage before you jump it. My bet is something is draining the battery over night. If the battery is drained in the morning then disconnect the battery and charge it up and check it a few hours later (don't hook it back up). Then if it's a drain issue then start the electrical diagnosis.

Jim, can you point me to where I can check apart from the battery cables?

I've put the battery back on the 8 amp charger and it is showing that it's holding only 4.7 volts. I'll do my best to check the ground points. I would have thought the drive back and forth to work would have kept me topped up if the battery was okay, but I get the point about locking the car and avoiding possible drain. Chicken or egg? Which came first? I believe the Interstate battery is about 2 years old and it comes with a 5 year warranty. I know it won't do any good to replace the battery and still have a drain.

If the battery is removed from the car and then fully charged, it'll be easy to determine if it can hold that charge as there is nothing to cause it to drain. Leave it out and check the voltage over a couple of days. If it holds that charge, then it's not the battery. It's something else that's causing it to drain when it's in the car.

It looks like there is a massive drain somewhere. I'm not handy with electrical issues. I got the battery charged to 12.7 v and when I reattached the cables you could see the voltage dropping on the multimeter down to 6v or so within a couple of minutes. No lights on, nothing on that I know of, nothing plugged in. Only have the trunk open (coupe) for the battery. I tried an old battery that charged to over 12 v and it also dropped down within a minute.
I've had no other issues, no event that could have caused this. Seems that putting a new battery in won't fix it - or am I wrong?

Regardless of what Autozone said, that seems like a worthless battery. For a GOOD battery to drain that quickly, the insulation on the battery cables would have melted due to the tremendous amount of current flowing.

What Jagtoes said. Pop the door open and turn on the headlights. If the lights don't come on bright you have battery problems. You should also have good voltage with the hatch open.

I lock mine each time I leave just to ensure the systems shut down quickly.

You have an XK8 too? How good is the battery in it? They should be the same size and might be the easiest test if that battery is reasonably good.

But as CJ suggests, a collapse of battery voltage usually suggests a battery that is not actually able to hold charge. Anything under 10v or so is regarded as scrap.

After I had the battery charged I reconnected the positive terminal and checked resistance between the negative battery post and the negative cable. It is showing -.87 ohms. Could have been from the trunk open and key fob, but that doesn't seem like it could be a huge drain. What is normal drainage for the clock, radio, alarm etc?

The XK8 has been sitting unused through the winter. I could pull and swap the battery in. I'm sure it needs to be charged and I'm not sure how good the battery is at this point. Good suggestion, thanks!

No headlights, if I reattach the battery after getting it up to over 12.5 v, the panel lights come on but go off in a minute or so as the voltage drops.