POWER:BAT: clarified the sign for the current fields

[Claudio-Chies]

Issue:

From the Message definition of BatteryInfo and BatteryInfoAux it it not clear if a discharge current should be positive or negative, which has lead different manufacturers to implement it differently, (E.g CUAV CAN power module, reports positive current for discharging, and TATTU Smart Battery reports negative current for discharging)
The same issue for the CUAV CBAT message, no units were present for any of the fields.

Solution:

• Added note at the end which aligns it with other dronecan messages
• Added units to the CUAV message

[MaEtUgR]

This is unclear in the original definition.

[Claudio-Chies]

Realized that the CBAT message suffers from the same issues, added units and definitions to it aswell.

[MaEtUgR]

Thanks for suggesting those too 👍

[Claudio-Chies]

@tridge would be happy for feedback