battery voltage on PB09 pin of U1

Hello all,

I'm hoping someone has insight into the code used to sense the battery voltage on pin PB09 of U1. The schematic shows a voltage divider of R8 (330K) and R9 (1M) wired to pin PB09 of the processor. Based on the divider values I see this will limit the voltage input on PB09 to 3.3V when the battery is at 4.4V. Clearly this indicates that the battery voltage can be read and utilized by a program. What is the name of the variable and/or is there some documentation regarding this? Many thanks.

Perfect. Very greatful.

Another part of my question had to do with documentation of this variable. Where can I find the listing of these global variables? I've tried looking into the "Hacking" section expecting to find the actual open source code running on the board but the GitHub reference doesn't seem to point clearly to this. Again, many thanks for any insight.

Once again, many thanks.