Battery sense for T-Echo

Copied battery stuff from RAK4631 to T-Echo
I got the voltage divider figures for T_Echo from SoftRF at
https://github.com/lyusupov/SoftRF/blob/master/software/firmware/source/SoftRF/src/platform/nRF52.h

I dont have a T-Echo so this code
HAS NOT BEEN TESTED

src/PowerFSM.cpp

@@ -299,7 +299,7 @@ void PowerFSM_setup()
     // On most boards we use light-sleep to be our main state, but on NRF52 we just stay in DARK
     State *lowPowerState = &stateLS;
 
-    auto meshSds = 0;
+    uint32_t meshSds = 0;
 
 #ifndef NRF52_SERIES
     // We never enter light-sleep or NB states on NRF52 (because the CPU uses so little power normally)

variants/t-echo/variant.h

@@ -251,6 +251,26 @@ External serial flash WP25R1635FZUIL0
 // To debug via the segger JLINK console rather than the CDC-ACM serial device
 // #define USE_SEGGER
 
+// Battery
+// The battery sense is hooked to pin A0 (4)
+// it is defined in the anlaolgue pin section of this file
+// and has 12 bit resolution
+#define BATTERY_SENSE_RESOLUTION_BITS 12
+#define BATTERY_SENSE_RESOLUTION 4096.0
+// Definition of milliVolt per LSB => 3.0V ADC range and 12-bit ADC resolution = 3000mV/4096
+#define VBAT_MV_PER_LSB (0.73242188F)
+// Voltage divider value => 100K + 100K voltage divider on VBAT = (100K / (100K + 100K))
+#define VBAT_DIVIDER (0.5F)
+// Compensation factor for the VBAT divider
+#define VBAT_DIVIDER_COMP (2.0)
+// Fixed calculation of milliVolt from compensation value
+#define REAL_VBAT_MV_PER_LSB (VBAT_DIVIDER_COMP * VBAT_MV_PER_LSB)
+#undef AREF_VOLTAGE
+#define AREF_VOLTAGE 3.0
+#define VBAT_AR_INTERNAL AR_INTERNAL_3_0
+#define ADC_MULTIPLIER VBAT_DIVIDER_COMP 
+#define VBAT_RAW_TO_SCALED(x) (REAL_VBAT_MV_PER_LSB * x)
+
 #ifdef __cplusplus
 }
 #endif