battery never fully charged

First off, it would be a BIG problem if the HV battery got to 100% SoC. Normally, if you have all the bars filled, you're at 80% SoC, but could be a few % over it. See Prius Palm Mileage Simulator. The graph does NOT represent 0 to 100% but rather only 40 to 80%. Prius tries to keep the battery around 60% or so.

One can get the SoC value in % with something like ScanGaugeII : Linear Logic - Home of the ScanGauge and adding an XGauge (I have one and have added it). There are other OBD 2 devices that can do it. You don't have to have a SG II.

The only times you'll see it hit 80% (full) is if you're going down a long hill. I used to hit that frequently where I lived in WA.

http://www.cleanmpg.com/forums/showthread.php?t=1224 was used for Hybrid drivers complete run for mileage mark.

 

Avoiding full is for battery longevity. That's why the display typically hovers around 6 bars and the entire capacity isn't actually displayed. Assumptions about charge-level and EV driving are common... and growing, due to the number of older Prius becoming used purchases.

You'll enjoy 100 MPG from time to time, but the point is to significantly improve emissions & efficiency... not electric only. In fact, that's true of even the plug-in model.

The engine will run when it makes sense. The system seeks out opportunities for optimal conditions and takes advantage of them. New owners sometimes unknowingly fight the system, cancelling out the benefit. For example, as the system runs to warm the coolant, it is also recharging the battery-pack... a benefit very easy to overlook.

Keep your eyes & ears attentive. You'll be impressed how well thought out the approach really is.