Define battery pin

src/configuration.h

@@ -327,6 +327,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #define GPS_RX_PIN 36
 #define GPS_TX_PIN 37
 
+#define BATTERY_PIN 35 // A battery voltage measurement pin, voltage divider connected here to measure battery voltage
+
 #define I2C_SDA 4 // I2C pins for this board
 #define I2C_SCL 15