I notice on my MFD that my battery level never fills up to the top. I've seen purple when it's low, blue, and green when it's in a high charge state, but there's always a missing 'never filled in' space for another bar, though always blank. I can let off the gas downhill with it already green and that blank space for an extra green bar never fills. It just stays blank. Is this normal?
Yup, normal. The car keeps the battery around ~60% nominally to leave room for regeneration. You aren't likely to see a filled battery display unless you brake your way down a relatively big hill. Plenty of people never see it in normal driving.
If you are on a steep long down hill, you SHOULD fill the bar after being on the brakes for 600 feet of vertical drop. At that point the engine starts roaring as it is used as an air pump to waste energy so the brakes do not overheat. I have never managed this in MS, nor do I expect you to near FWB, but if you vacation in the Great Smokeys you can get to this point. Tail of the Dragon at Deals Gap and Cherohala Skyway, Graham Co, NC [My youngest brother was an EWO near FWB and still lives in the area]
If someday you do want to get to that magic spot, the key, if you don't have a mountain hill to deal with, but are, let's say, coming to a stop at the end of a hill anyway, is to apply the brakes gently and gradually over a longer period of time, so that you're slightly slowing, or, down a steep hill, that you're even maintaining speed with the regen brakes on. If you push too hard, the friction brakes come on. If you go over a bump and the traction control engages for a second, it will turn off most regen even if you release the brake for a second and re-apply (I don't know the exact time needed off the brake to get the car back in regen mode). For max regen then, longer, gradual braking is good, and personally I release the brake preventively over bumps and reapply right after to avoid the possibility of losing regen capability. P.S. Just noticed the Florida part...good luck