My battery seems to be draining quite quickly and I thought I might have messed something up with my recent stereo install. I measured my X300, and also my dads for comparison (his is 100% stock).

Everything was off, and I waited until the trunk lights had switched themselves off.

I couldn't put the thing around the positive leads, so readings are negative. I switched the dial on the metre to "40A":

My car: -00.18

Dads car: -00.14

Pretty much the same... So I suppose that means there is nothing wrong with my one?

 

I don't know what an expected 'sleeping' current draw is for an X300. Probably good to know though!

A lead acid battery needs to be kept up to full charge level. Once your voltage drops too low, the battery suffers damage to one or more cells. First off, have your battery tested. A damaged battery will loose its charge much more quickly and only compound your frustration. Once you're sure your battery is good, be sure to keep it charged and properly filled until you know it won't be drawn down again. Put a trickle charger on it every day if necessary!

Your car is pulling 40mA (about 30%) more than your dads...but again; what should the draw really be?

In any case, to hone in on where the current's being used, pull one fuse at a time while observing the current reading. You will find where it's being used that way. I'd start with a fuse chart and pick the ones you know should be active when the car is supposed to be 'asleep'. Pull one at a time while observing and put it back before moving on to the next one.

Hope the hunting is fruitful!

 

Just checked my "sleeping" X300, and 00.17a is my reading.

The "older" XJ-S, is 00.14a. B

Both batteries are less than 2 years old.

The XJ-S battery that was replaced was 8 years old, and "dropped" a cell, dead as, and push starting an XJ-S is just NOT fun, hahaha.

Recently spent 3 weeks in Vegas, and "forgot" to unplug the batteries, it will happen to you as the numbers get higher, and both fired up first crank on our return.

Also I am fairly **** about keeping the batteries "topped up", and a charger is put on both cars every month for an overnight charge.

I reckon you got a battery that is dying. Down here we kind of think that 1 year past the warranty time allowance, and you are blessed.

 

Forgot, I do that.

You could always 'nick" Dads battery and see if the fault stays with your car, or follows the battery. I would NOT do that unless you can run a lot faster than Dad.