Battery sucked dry in just 2 hours

Hey guys,

My 96 4.0 AW4 242 - started great yesterday, started great this morning, parked for 2 hours, just a weak click and battery is down to 6.5 volts. I did not leave the door open or lights on and nothing was running - no radio, no interior light, no nothing.

The battery in not old and got a full charge and load test on the bench two months ago when I put in a new alternator. Guage when running shows 14 volts, 13.8 with the meter, and guarge was reading fine this morning and last night.

Factors I can think of:
- blower motor has been getting chirpy in the last couple of weeks and sometimes has faint burnt motor odor (definitely not coolant smell.)
- This morning it started up strong (as always) but when I turned on the lights, I got no lights. Turned off, turned on, no lights. flipped the hi/low switch, they came on and then all switches worked normally (on/off/ hi/low, etc.)
- if I wack the bottom of the steering column with my knee while driving, I will lose power for a split second (been meaning to fix that, happening since I got it.)

I am charging the battery now and have my ammeter to check for a parasitic draw from the batt with power off as soon as I have 12 volts from it.

Anyone have any thoughts on which avenue I should explore first if I find a high draw?

Interesting. Same exact thing happened to me this morning, a few minutes with a pair of jumper cables fixed it right up. I didn't even get a click, and my battery measured under a volt... it's less than 2 years old and has been working great for weeks.

Once you find the parasitic draw it's pretty easy to figure out, look in your FSM and see what is on the fuse or wire you found the draw in. I have a 96 FSM (got it for my 96) if you need anything looked up.

I've got a 95 FSM and also a 97 FSM that I found a couple weeks ago at the local flea market book bin for the mix & match 96. Depending on what I'm looking up one or the other usually has the answers.

To verify a parasitic draw, fully charge the battery, then remove the cables and come back in a few hours to see if the voltage holds. If it does, hook an ammeter from the positive terminal to the positive cable and measure the current. It should be less than .050 amps.

I was just looking at my meter, it has a 10 amp fused limit for DC current (usually used for testing battery backup and emergency lighting systems)

I don't think that should matter - drawing more that 10 amps while not running would be a more significant issue than changing a fuse in my meter.

I've had batteries permanently die on me without any indications of problems. The last time it happened, I had been running around in the Jeep all day. Last crank of the day...nothing. Sometimes it just happens.

Well, I was right that my 10 amp limit should be more than enough - on the other hand it's pulling 5.8 amps.

I will start pulling fuses now, but if you have an idea what could be drawing this much let me know.

Yikes! Yeah, that will do it.

Check your glove box light and make sure your ignition switch isn't keeping the "run" or "accessory" position powered at all times. Seems like something of that nature might be at fault since you mentioned it's a little flaky in other ways.

This is why I need an assistant. As I would check with the meter and then pull a fuse, then check with the meter etc... it was not until the daylight fades that i realize the interior lights are coming on when I jump the meter leads to the batt terminal and connector.

The switch is shorted internally. The interior lights are coming on, switch is off. Connectors look OK.

6 amps for the inside lights. There are 5 of them, but Wow.

swapped headlight switch with a spare from the nogo XJ scrap heap.

draw is now .04 amps with key off.

Yay!

BrokenSockets said:

This is why I need an assistant. As I would check with the meter and then pull a fuse, then check with the meter etc... it was not until the daylight fades that i realize the interior lights are coming on when I jump the meter leads to the batt terminal and connector.

The switch is shorted internally. The interior lights are coming on, switch is off. Connectors look OK.

6 amps for the inside lights. There are 5 of them, but Wow.

Click to expand...

And that is why I will check for parasitic draws with a 12 volt test light or a taillight bulb. A "normal" draw of 50 mAmps or less will only make the test light/bulb dimly glow. A heavier draw will make the light/bulb glow brightly. With that setup you can be at the a**end of the vehicle and be unplugging sections of harness and see the light go out--saves running back and forth to check the meter.

Just a stubborn old school kind of guy.

I had an extreme draw of 6.85amps with all doors closed. Turned out to be my power antenna. Crazy that it could draw that much.

I like using a test light too, Also have an old seatbelt buzzer with a couple leads on it. Works good when you looking for a couple volts or more and can't see the light