Plugins: Battery: Chose first battery as primary in multi battery devices

For devices with multiple batteries such as the PP/PPP the primaryDevice is currently set to the last battery device which on the PP/PPP it ends up being the keyboard battery, this makes it so it will use the first battery in the list instead which is the actual PPP battery. Perhaps a more robust solution should be considered in the future or one that will return all batteries with history/statistics and graph them all.