like tittle says im so sick of battery dying over 2 days of no starting the car. I put in a new battery and it gradually dies over short period of time (2 month) im replacing with decent battery 1000cca. first couple of weeks of replacing battery car cranks very nicely but gradually goes cranking slower, I can notice the change in cranking speed. then battery starts dying if i leave the car parked for 2 days it will crank so slow it will not start and battery dies. I can give the battery a full charge and will do the same again. this must be a MASSIVE drain on the system when car is off. or could the alternator be bad even tho it has no problems when the car is runing?

 

There must be something staying live other than the normal stuff.

But what it is will take time to find

 

Many things could be hissy, but the X300 is NOT known for this in the real world.

I had this with one of our S Types, and I simply did an amperage draw measurement when the car was supposedly asleep, and found 1.5amps, and that was simply the small "gate switch" of the ignition barrel stuck in the open position, thus preventing shutting down of the various modules. Fixed with some silicone spray, all sweet.

I suggest disconnecting the -ve terminal, and connecting a DVM (set to amps), between to battery post and that cable, and note the amp draw that appears on the screen.

If this is higher than about 100 miliamps then begin unplugging fises one at a time until the culprit is found.

YES, the alternator regulator could be draining to earth, not so common on the Hitachi units, but anything is possible. Unplug the alternator if in doubt, careful with the wires, that they dont short out on the surrounding metalwork.

 

I can't say enough good things about Priority Start modules. Always leaves enough starting voltage so you're never stranded with a dead battery. I've had mine since 1998 & no dead batteries.

PriorityStart - Stop Dead Batteries on Cars & Boats [Priority Start! Battery Protector]

 

I just posted a thread with this similar problem. I have a 1996 Xj6 and it looks like all my dashboard lights stay on as though the key is in the accessory position even though it is pulled out.

Sounds like maybe I am having the issue one of the above posts speaks of with something sticking in the ignition switch? I can charge the battery and it starts fine for a few days at best but then once left over the weekend it is completely or near to completely dead.