Looking in the source code of the DR, there seems to be a gasgauge IC on the DR1000 (kdbupgrade.c). The gasgauge ic probably contains its own CPU which needs to be programmed to monitor the charge/dis-charge cycles of the battery (The source code uses a block of 1024 bytes that needs to be transferred to the gasgauge ic). I assume that this program (or its parameters) are tuned for the specific battery used by the DR. So using a battery that is different enough from the original battery probably will not work. Which is in line with the outcome of the experiments described in this thread.
Unfortunately the pictures on http://dr1000s.blogspot.nl/
do not show anymore, so I could not find any details w.r.t. the used gasgauge ic.