I once stored my Pro-2006 for three years with a Duracell that was most likely new when I unplugged the scanner. This was during some moves for the military where I had the scanner in storage. There was no battery leakage and the memory was retained for that time. Although I moved to a different part of the country and had to buy a different frequency book at the local Radio Shack store. 1996-1998 timeframe.
As for the backlight on the display, I always use the dimmer setting and that has probably prolonged the life of the light.
Great scanner for the desktop. I still use it today for testing radios and gear where there is no trunking, Trbo networks or anything digital. Great scanner even today.