To get an idea about the current status of your batteries, there are a few apps available:
To install, unpack the downloaded zip file and transfer the files to the SD card. With the SD card in the HP 50g, use the integrated file manager to move them to the FLASH folder. Then reboot the calculator (press ON+F3 to soft-reset).
You can then access them from the LIB (↱ 2) catalog.