Sigh. Just went to go out in the truck and the battery was completely drained. Hadn't used it for over a week.
Seems to happen every now and then (although this was the first 100% drain). But very intermittently.
I think it's something the computers decided to just leave powered every now and then, it's not lights left on or anything obvious.
Battery passes tests, so I don't think it's that.

Anyone have any ideas? I really can't think of where to begin to track this one down.

 

Sounds like you have a parasitic drain. The clock and security do slowly drain the battery but they shouldn't in one week. Have you tried measuring the amount of millivolts or milliamps normally used when switched off vs the current drain when switched off. Additional USB, computer or phone sockets can and are infamous for draining and causing a parasitic drain.

 

First, you need to have an actual battery test performed as well as an alternator test which has to show a charging voltage, with all lights on, between 13.6 and 14.4 volts at an idle. Usually once a battery has died a couple of times, it is no long good.
If both of the tests are good, then yes, have some one test for a voltage draw.

 

How does one test that? I'm guessing equipment I don't have...
I do have usb that's supposed to loose power when the seats do, but I'm never really convinced that it always does. Timers and linked to the driver's door make it hard to feel 100% sure.

And thanks guys! Appreciate the help.

 

Your signature says that your truck does not have air suspension. Did it have air suspension originally that was changed over to coils? If so a setting must be changed in the SLABS computer so that it knows the air suspension is no longer present. Otherwise it will, from time to time, try to run the air suspension pump, etc., which can drain the battery. That was the case with my truck.

 

Check your ground. I had this happen a while back and relocated the ground to the accessory bracket so I can keep a better eye on it.

 

I've tracked one down doing the following.

Remove the live battery terminal. Make sure ignition is off. Or the position when it's draining power.

Clip a multimeter between the battery post and the cable and measure milli amps. You should get a reading.

Make sure not to turn anything on that will blow your meter.

Start pulling fuses until the reading drops significantly. This should indicate what circuit the drain is on.

Used this method on other vehicles. Not LR. Not sure if there are any quirks that would make it problematic with a Disco.

Thinking about it, it might be better to use the negative terminal. (A more sparky type will chime in on that I'm sure. )

 

You could try unhooking one side of the battery. (I prefer the ground side for shorting reasons, but it will work on either side). Then hook up an ammeter between the disconnected cable and the terminal. With the key off and nothing on in the truck, it should read no more than about 50ma. If it's higher than that, you can remove one fuse at a time until the amperage drops. When it does drop, you've found the item that is drawing on the battery. Just make sure you disable the interior lights so you can open the door to take out the fuses.
Also, if you don't have a draw of over 50ma when you first hook up the meter, more than likely, your battery is no good or not charged properly.
Good luck, I hope you find it without too much trouble!

 

Beat you to it...

 

LOL! You beat me by one minute!
I use the negative cable so i don't have to worry about the cable accidentally touching anything metal and shorting out while testing. Even if it didn't kill the vehicle, your multimeter may not fair so well.