common: added voltage and current multipliers to BATTERY_STATUS

[tridge]

this is to allow for vehicles with very high voltage and very high
current power systems. Vehicles with more than 65V ESCs are becoming
quite common

[peterbarker]

@hamishwillee for visibility

[peterbarker]

@auturgy for visibility

[WickedShell]

I don't think this is a great idea. Mostly the message is already large, but because there is also some misunderstanding here. The message can already support upto 917 V, as long as you aren't doing per cell monitoring. (Per cell obviously caps at 14 cells of 65V each). You simply fill in the maximum valid value allowed per cell until you have added up to the right battery. Ardupilot already supports this. The current handling is more problematic, but do we have an example where this has been exceeded, or is this just trying to cover for future cases? Part of my concern here is the message is already ~15% of my bandwidth on a default RFD at 57600. Making it bigger gets painful quickly with multiple battery monitors.

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[hamishwillee]

Can we please have PRs to common.xml in mavlink/mavlink repo.

@WickedShell Sounds like a good point. Last time we tried to change this message we were already at the point of "perhaps this needs a fresh start".
What other options are there?

We can discuss it in the MAVLink dev call

[hamishwillee]

PS. I also just got a request for additional 2 cells to be added: mavlink#1747