BMW Repair: interemittent startup/battery wont hold a charge, rear trunk, current meter

Question
5 bmonths ago my 6 yr old 540 had slow transmission due to a dead batter(low voltage levels). New battery was fine for 4 months, then my mechanic said it was the alternator and replaced this. Two weeks later battery was dead again so he put in new battery. One week later "Transmission Fail Safe Progr" light came on and no lights and couldn't jump start. Is this a short somewhere? a fuse? i saw earlier response to  using an Ohm meter.
thanks!

Answer
Hello ED,
A current draw test is your best diagnostic bet in cases like this. But first you have to remove the battery or at least remove the negative and charge it fully (and confirm that it is really fully charged). Then connect the battery with the key in off position. Never jump or connect batteries with the key on for the current surge would damage control modules.
Next make sure that all accessories are off including lights, etc.(front hood must be closed or hood position
switch must be pulled out, rear trunk lock must be locked
although trunk need not be closed).
Then connect a current meter that can read down to milliamps. Allow car's computer system to wind down and go to sleep (this usually takes 16 minutes but give it 20). Then read current draw continuously for a period of 30 minutes noting down minimum, maximum and average. Average is not minimum plus maximum divided by 2. Current draw must be approximately 25 to 45 ma, but 50 to 60 can be allowed.
Very short spikes of 60 and above is permissible so long as it is really very short (measured in milliseconds or a few seconds).
If current draw is above maximum specs, localizing the source can be done by removing the fuses one by one and noting if the current draw drops (obviously, the car is awake during this process). It is a tedious process. And it is meant to diagnose only parasitic draws. You still have to use other methods to check battery health and alternator functioning. I have seen many instances of battery going dead due to aftermarket electronic installations, like radios, amplifiers or burglar alarms (even leaving an ipod adapter/transformer attached to the lighter socket). This happens because the car's computer does not go to sleep due to the said accessories.
Taking off the battery while it is being charged would probably reset computer modules and allow you to restart the vehicle when the battery is later installed.
Tino