I have been having problems with my 2001 E53 for a long time.
If I don't run the engine for a day or so then it won't start.
Turn the key and it just clicks. attach a booster battery and it starts first turn of the key.
Reading the forums it seems I should have somehow registered this battery with the ECU when I bought it 3 years ago. I bought the battery because of the starting problems. I had the battery checked by the parts supplier and they say it is fine (i think they sold me the battery with insufficient CCA, as there is another battery with higher CCA available for Canada).

However, as the battery dies at the slightest excuse it is causing me some problems with the MIL.

Last week i fixed the window carrier and during the 40 minutes or so that took with the door open the battery was absolutely flat. i.e. it didn't even do the usual click click sound. (it has NEVER turned over slowly, it runs or clicks).
I boosted the battery which required the booster pack to be attached to the car for a few minutes before it turned over.
The MIL has not gone out.

Using a Scantool OBDII laptop software i cleared the codes (24 of them from incorrect system voltage to incorrect gear ratio in all 4 gears, none of which are genuine i'm certain as it has done this before).
After repeated attempts to erase the codes, i.e. codes cleared but then returned immediately the engine started i called a friend who has the all singing all dancing SnapOn OBDII scanner.
He erased the codes but the MIL still wont go out even though the snap on has confirmed there are no codes stored.

It seems there might be a 20 pin DLC in the engine compartment that needs to be accessed too.

using the VIN analyzer the car was built 2000/10/06 which i think is October 6th and so probably too late to have the 20 pin connector. In any event I can't find one.

So, can anybody tell me the location of the DLC in the engine compartment.

Does anybody have any insight into erasing the MIL?

Typically, I have a buyer for the car but have to get it emissions tested first, which can't be done with the MIL on.

Any help at all is greatly appreciated.