The battery indicator on my DX90 decreases with use on Mango. Haven't tested with the current build, but with older builds of Rockbox it just hangs out between 90-100% and never goes below that no matter how long I've used it. However, if I boot back into Mango the battery indicator shows depletion correctly.
With similar code I know the battery indicator does not work way back in DX50. But I only started to look at the battery indicator in DX90 since the latest build. I saw it go all the way down to 0% and shutdown after a couple of minutes after that.
The latest build actually prevents DX90 from going to sleep state (which I found is contributing to the crackling noise that appears randomly). it only turns off the backlight when idle time is triggered. I believe that may have influence on how the battery indicator work on DX90.
EDIT: Just got mine below 90% and still counting down.
Edited by headwhacker - 8/16/14 at 7:39pm