prepare LMIC battlevel MAC request

include/power.h

@@ -11,6 +11,10 @@
 #define DEFAULT_VREF 1100 // tbd: use adc2_vref_to_gpio() for better estimate
 #define NO_OF_SAMPLES 64  // we do some multisampling to get better values
 
+#ifndef BAT_MAX_VOLTAGE
+#define BAT_MAX_VOLTAGE 4100 // millivolts
+#endif
+
 uint16_t read_voltage(void);
 void calibrate_voltage(void);
 bool batt_sufficient(void);