     Wire.write((byte *)(&status), sizeof(status));
     break;
   case REGISTER(BOARD) + BOARD_BATTERY:
-    // V = analog / 56.88
-    // Range = 10.6 .. 12.6
+    // centiV = analog * 1.7581
+    // Range = 10.6V .. 12.6V
     value = analogRead(PIN_ANALOG_BATTERY);
-    Wire.write((byte)(((float)value / 56.88 - 10.6) * 50));
+    Wire.write((byte)(value * 1.7581 / 2));
     break;
   case REGISTER(LIGHT_SENSOR):
     value = analogRead(PIN_ANALOG_LIGHT_SENSOR);

  Wire.onReceive(i2cReceive);
  READY(BOARD);

  environment_sensor.begin();
  // not: READY(ENVIRONMENT_SENSOR);
  // (do not make it ready until the first measurement)

#define PIN_ANALOG_I2C_SDA      4 // i2c enabled by jumper
#define PIN_ANALOG_I2C_SCL      5 // i2c enabled by jumper

#ifdef DEBUG
#  define Log Serial.println
#else
#  define Log(...)
#endif

// TODO: read these from Arduino Nano (protocol = ?)
unsigned long encoder_left_front = 0, encoder_left_back = 0,
              encoder_right_front = 0, encoder_right_back = 0;
