Function getBattery not found on iTracker RAK 8212

@Kartman, w/ nMosFet something like this:

`
VBat -----------------------+--------+-------­-----+----
            .-----------.   |        |            |
            | 3..3.3V   |   |       .|.           |
3..3.3V -+--+ Voltage   +---'       |R|           |
         |  | Regulator |           |E|           |
         |  '-----+-----'           |S|           |
         |        |                 |1|           |
ESPRUINO |        |                 '|'           |
iTracker |        |         nMosFet  |            |
.--------+--.     |        .--------.| D          | +
|           |     |       /          |         _______
|           |     |      /           |\          ___
|           |     |     .            | .       _______
|   nMos-   |     |   G |     | |----' |   Bat   ___
|   Fet     +-----------+-----| |<---. |       _______
|   driving |     |     |     | |----| |         ___
|   pin     |     |     '            | '       _______
|           |     |      \           |/          ___
|           |     |       \          |            | -
|           |     |        '--------'| S          |
|           |     |                  |            |
|    Analog |     |                  |            |
|    read   +------------------------+            |
|    pin    |     |                  |            |
|           |     |                 .|.           |
|           |     |                 |R|           |
|           |     |                 |E|           |
'-----+-----'     |                 |S|           |
      |           |                 |2|           |
      |           |                 '|'           |
      |           |                  |            |
GND --+-----------+------------------+------­------+----
`