What do the different colors on the battery icon mean?

The battery icon in the top, left displays the charge level. If the color is:

Blue = displays level of charge. 

Gray with "?" = no SatPaq has been selected.

Gray with "Z" = SatPaq is asleep.

Red = battery is very low and should be charged soon.

You can also tap the battery icon to view information about the SatPaq and SpaceLinq.