t1000 : power bat sensor only when necessary

src/helpers/nrf52/T1000eBoard.h

@@ -29,9 +29,12 @@ public:
 
   uint16_t getBattMilliVolts() override {
   #ifdef BATTERY_PIN
+    digitalWrite(PIN_3V3_EN, HIGH);
     analogReference(AR_INTERNAL_3_0);
     analogReadResolution(12);
+    delay(10);
     float volts = (analogRead(BATTERY_PIN) * ADC_MULTIPLIER * AREF_VOLTAGE) / 4096;
+    digitalWrite(PIN_3V3_EN, LOW);
 
     analogReference(AR_DEFAULT);  // put back to default
     analogReadResolution(10);