Should be nice if an update that will shows the information about the Battery life remaining on the VARIA RADAR in Percentage (%) via a data field.
I see there is an IQ app called Tail Light Field. It adds a data field to show the light status and allows turning the light off and on. The app also includes a data field for battery status - screen shot shows a battery icon with 5 bars to show state of charge rather than % but might be close to what you are looking for
It is not really possible to show the battery life as a % as that data is not available over the ANT+ battery status message.
The condition of the battery is not reported as a %, but rather as a status code. You could try mapping codes 1 through to 5 to a %, e.g. 100,80,60,40,20, but you would be limited to steps of 20%. This is what the battery icon is doing,
There's also one integrated into this data field.