I just upgraded my '800 to the newest firmware, and noticed a big change in the operation of the battery icon.
After installing a freshly charged set of NiMh cells, the battery icon started to drop after the scanner had been running for only 10 minutes! It continued to drop steadily, taking several hours, until the battery icon was just an outline. This is the first time I have seen the battery icon down this low. The scanner continued to run several hours after the battery icon indicated empty. This is in contrast to the way the icon was prior to the firmware update. Prior to the upgrade, the icon would remain full for a couple of hours, then slowly drop, and the scanner would cut off with the battery icon still displaying about 1/8 full.
I have changed the battery voltage settings as others here have suggested. From the default 4.95 volts at 14 bars to 4.85 volts; and from 4.33 volts for the alert to 4.1 volts. I changed the "in-between" settings each down a bit also. The icon battery indicator seems to be operating more smoothly and accurately (so far!)