I'll start off by saying I'm sure I have a weak battery.. if the temp drops below freezing my car usually won't start at all.. but if i wait a few days and the temp goes back up it will start.. that being said..

I parked my car.. through the night the temp dipped to about 40 at night.. the next morning I go to start my car and it is completely dead.. no dash lights.. nothing.. I take the key out... put the key back in and try again.. dash light comes on and car starts up fine.. started it up at 9am .. but the clock reads 1:45.. as if the battery died in the middle of the night.. but yet it started right up after taking the key out and trying it again.. how concerned should I be.. I don't want it to short out while I'm driving down the freeway..

 

First replace the battery. Then see if your problem is still there.

 

also check the main harness to the ecu.

 

i had a similar problem and it ended up being corrosion on the inside of the battery terminal i just cleaned them up real good with a wire brush and been fine since. check that you have 12v across the battery terminals and also to your fuse box under dash.

 

You need 12.6v across the battery, and when you crank the car it should not drop below 9.6v at anytime during the cranking, otherwise you have a bad battery. If you disable the ignition, and fuel, you will get a better reading on the condition of the battery. How old is the battery? Is it a maintenance free battery? or one that uses water? All this plays into to how the battery is, and if its time to replace.

 

I had a similar problem a few years ago, turned out my battery posts were corroded. Give em a clean and tighten them terminals up. If your car starts fine most days but then suddenly won't start one day, this is most likely the problem.