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A friend of mine has an IBM Micro drive 340mb. He has offered to let me try it.
How many times faster will the battery go with a drive over a CF approximately?
Actually the 340Mb use slighly more power, but is faster @ startup than the 1G. You'll notice this with some cameras that the drive is ready before it takes the time for the camera to intialize. Most of the current surges occur when the microdrive is writing, the rest of the time it goes into the idle mode and save on the battery.
Your mileage varies: for example I can almost fill the entire microdrive in an hour with one set of battery in the studio (using an external strobe for sync), or I need 2-3 sets of battery to accomplish the same feat in a 12hr period...
Another thing to consider is with the larger capacity of the microdrive you'll be just storing pictures(ie keep everything for later use) instead of reviewing and deleting pictures on the smaller cards which actually drain the battery more, since the camera processor has to do all the work.

ops: Also remember with flashes the device can not erase one location, but an entire block has to be erased and rewritten (hence the write cycles multiply very quickly, all done by the internal controller unaware by the end-user)!