Voltage Drop when keyed on

Went to start the jeep this morning and got nothing. Here is what Ive discovered. The battery has 12.3 Volts with the key off, when i get in the car dome lights work, key buzzer works. As soon as I put the key in the on position the dome light dims, and I get no radio, locks, windows, ect...

With the jeep in the on position I get somewhere around 3-5 volts at the battery, as soon as I turn the key off it takes a few seconds and voltage jumps back up to 12+

What could be causing a massive voltage loss just keying the vehicle on?

Here is some more info and readings showing the drop. Odd thing is the vehicle will not recover to 12V until the door is shut, but opening and closing the door do not affect the voltage by itself. IF you leave the door closed when you key off it goes back to 12 volts, not quickly but within a few seconds.

It was doing a similar thing a while back and we changed the terminals and it seems to have went away.

Car Off, Doors Shut

http://www.flickr.com/photos/31401781@N00/4878453789/

Door Open

http://www.flickr.com/photos/31401781@N00/4879062830/

Key to first position, Door Open

http://www.flickr.com/photos/31401781@N00/4879062880/

Key On, Door Open

http://www.flickr.com/photos/31401781@N00/4878453933/

Key Off, Door Open

http://www.flickr.com/photos/31401781@N00/4879062962/

Key Off, Door Shut

http://www.flickr.com/photos/31401781@N00/4879062994/

If you are measuring directly on the terminals and not on the wiring, the battery is definately bad. To pull a battery down that far would mean pulling over a hundred amps, which translates to 1200w of heat. That is enough to smoke even a large starter cable. So if you aren't getting smoke, the battery is bad.

Yes measurements were taken from the terminals After cleaning and terminals I was able to get power in the on position but for a short time, right now i have the battery on a charger and then i will take to the local shop and have it load tested.

Well im pretty sure its a bad battery, I pulled the battery put the charger on it and when it said it was full, I was only reading 10.5 volts now. Not surprised the battery was MFG in 07 so its 3 years old and its a 3 yr warranty battery.... go figure....

old_man said:

If you are measuring directly on the terminals and not on the wiring, the battery is definitely bad. To pull a battery down that far would mean pulling over a hundred amps, which translates to 1200w of heat. That is enough to smoke even a large starter cable. So if you aren't getting smoke, the battery is bad.

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X2 listen to the old_man on this one. That is dropping way to much for what is going on. Have your alternator tested as good measure to. Mainly to make sure that the diode is still ok. If the diode is bad it can/will kill a battery by letting the small amount of a/c voltage that the alternator generates go at the battery which can kill it right quick. Most parts stores can do the alt test in the vehicle while the vehicle is running as long as you have a good battery in there when you are getting it tested.

ReverendOD said:

Not surprised the battery was MFG in 07 so its 3 years old and its a 3 yr warranty battery.... go figure....

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3 year free replacement plus prorate or just a 3 year warranty period. Our batteries at O'Reilly's are offered both in a 72 month(first 2 years its free replacement + after that it is prorated) then we have an 84 month battery(3 year free replacement then prorated after that).

So if there is prorated on the battery the longer you own it past the free replacement period the more you pay for it. So if it was just over the free replacement period you should be able to get a replacement at very little cost. If you are the original purchaser of the battery that is.

No battery was in the vehicle when i bought it and he didnt keep the recipet. Then again it was a Walmart battery might be worth taking it in and seeing what they say.

We did put a spare battery in and it fired right up... guess its time for a battery.

A battery voltage of less than 12.6 implies a discharged, but not necessarily a "bad" battery. First, recharge the battery with terminals disconnected (insure correct electrolyte levels in each cell). It should reach ~13.8 to 14.2 volts while charging. Second, let the battery set overnight, and check voltage. If the battery holds the charge, you should get a reading equal to, or greater than 12.6. If true, then you need to determine what's causing the battery to drain while connected to the vehicle.
If you merely replace your battery without doing a complete checkup of your electrical system, and the problem was not the battery, your problem will repeat itself.

pulled the batter tossed it on 2 chargers both showed charged and it would only hold 10.4 volts...

Sounds an awful lot like one of the cells is shorted / dendrited. Time for a new one...

(lead acid cells are ~2-2.1 volts each, there are 6 cells in series in your car battery)