Updated battery status message (mavlink#1299)

Co-authored-by: Hamish Willee <[email protected]>

message_definitions/v1.0/common.xml

@@ -4793,7 +4793,7 @@
       <field type="uint8_t" name="battery_function" enum="MAV_BATTERY_FUNCTION">Function of the battery</field>
       <field type="uint8_t" name="type" enum="MAV_BATTERY_TYPE">Type (chemistry) of the battery</field>
       <field type="int16_t" name="temperature" units="cdegC">Temperature of the battery. INT16_MAX for unknown temperature.</field>
-      <field type="uint16_t[10]" name="voltages" units="mV">Battery voltage of cells. Cells above the valid cell count for this battery should have the UINT16_MAX value.</field>
+      <field type="uint16_t[10]" name="voltages" units="mV">Battery voltage of cells. Cells above the valid cell count for this battery should have the UINT16_MAX value. If individual cell voltages are unknown or not measured for this battery, then the overall battery voltage should be filled in cell 0, with all others set to UINT16_MAX. If the voltage of the battery is greater than (UINT16_MAX - 1), then cell 0 should be set to (UINT16_MAX - 1), and cell 1 to the remaining voltage. This can be extended to multiple cells if the total voltage is greater than 2 * (UINT16_MAX - 1).</field>
       <field type="int16_t" name="current_battery" units="cA">Battery current, -1: autopilot does not measure the current</field>
       <field type="int32_t" name="current_consumed" units="mAh">Consumed charge, -1: autopilot does not provide consumption estimate</field>
       <field type="int32_t" name="energy_consumed" units="hJ">Consumed energy, -1: autopilot does not provide energy consumption estimate</field>