Yes, absolutely normal. The regular Prius targets six out of eight bars. If you have more than this, it will try to use more than normal to get rid of the excess - it's so it has somewhere to store energy produced by braking. If the battery ever does get up to 8 bars it (reportedly) starts running the engine as an air pump to waste energy! The lower the charge level gets, the more determined the car becomes to recharge back up to 6 bars. Even then the battery meter is a false reading - there's still about 40% charge remaining when the meter shows no bars at all, and eight bars really indicates about 80% charge. Restricting battery usage to this range extends the battery's life substantially. I've now owned my car for over four years and I've never seen 8 bars, nor had the forced-discharge behaviour, but then I've never done a long mountain descent. On my car, with the colour Multi-Function Display, the battery meter is pinkish-red for one or two bars, blue for three to six, and green for 7 or 8.