Will, the best thing you can do is bring the car to an Indy and get the fault codes interrogated, see if there is a recurrent root code, make notes, clear the faults and maybe bring it back after a few days to see if they've logged again.
Voltages seem fine, the drop between the battery and engine terminals is other parasitic components causing the voltage drop. It could be worth having a look in the wheelhouses for damaged ABS / DSC (and Tyre pressure monitoring) sensors / cables - does it happen when wet / dry both etc - it could be a DSC pump or pre-charge pump - it could be any number of things, the components share a bus system and often interfere when they're not tip top.
To rule out the battery fob, have you tried using another key or have you just the one?