1. Power on, with a _good_ voltage./1
2. Set power door locks as "unlocked"./2
3. Hope to God the trunk key cylinder slot is vertical .:. unlocked from the perspective of the owner - which it already was; so I apparently don't _need_ a master key.
4. Use the button under the trunk overhang trim to unlock the trunk - yay!/3
Ok, so the BMW fans are quietly amused at my travails, but they must consider them to be some sort of 'initiation' to the joys(?) of Bimmership, right?
/1: yesterday I left a large capacity battery connected by jumper cables to the charging points in the engine compartment for almost two hours, while I emptied the trunk through the access panel. When I left, the last thing I did was check the panel lights by turning on the key; there was just a dim illumination of one light on the dash, but that was much better then before. I think the battery took just a little charge as the batteries balanced themselves - which is a good sign. I again charged up the jump battery last night, so I started with a good jump battery today. I connected it to the car, and the lights are much brighter now; so I'm hoping the voltage is close to correct.
/2: When it was running last week, I know I set the doors to "unlocked", as all the pins popped up. Today, the door lock pins didn't move at all when I used the switch from unlock, to lock, to unlock again, twice.
/3: I know I tried this button last week after I unlocked the doors. Not sure if the car was running. Also not sure if the car was energized with the key, though. _That_ might be the ticket. I'll verify and clarify tomorrow.