Hello. An alkaline battery discharges at a slow and predictable rate. Most rechargeables continue to provide a constant voltage until the point that they have almost nothing else to give. Therefore, the bookport cannot track the slow decline in battery voltage to tell you how much battery life you have left. I use rechargeables all the time, and when they get down to about 20%, I replaced them. Even if you let them run completely down while using the bookport, you still get the message that you should replace your batteries. I've never lost any data as a result.
Gary
