Full charge going downhill. (regen overcharging)

Toyota has designed the system so that overcharging the hybrid (Traction) battery is avoided, by spinning the ICE with the fuel switched off to provide a load so that the regen is not being stuffed into the battery. (Smart folks, those Japanese! )

…so the answer to your original post is…
Don't worry! Be happy!
…as you sit and wonder at the quietness of your amazing Prius!

 

As Wil said, it has an engine to spin rather than load resistors. The excess strain or wear goes to the engine, not the battery.

If practical, try to halt the recharging at something less than 100%, with enough shortage to soak up that initial downhill run. This will reduce engine wear, and additionally reduce battery stress by having it spend less total time (no parked time at all) at 100%. Not yet having a PHEV myself, I can't tell you how to set it to stop recharging early. The amount of charge space to leave unfilled will have to be figured out by trial and error.

 

I thought the 100% was not really 100% so to avoid those problems.

 

Here is what I have noticed. Since it is winter, my EV mileage has dropped considerably, most likely due to using the heater. I live on a hill above our town and it is about two miles downhill until the flat land. Today I started with 23.6 miles on the HUD. As I left our neighborhood, about a mile down hill, it had increased to 23.8 miles. This is after fully charging last night. It stayed at 23.8 for the next two miles, then started decreasing as usual. This tells me that the software stops the home charging at some point well under fully charged. This allows an additional charge to happen from the onboard generator, rather than wasting that charge. Of course, I am not an expert on the Prime charging system, but I was once a Navy Master Chief Electronics Technician, so I remember enough to be dangerous!

 

That reduces, not eliminates, the problem. You can do more.

 

don't worry, be happy.