Strange battery and regen braking behavior

We live at 6300 feet in Colorado and often drive to higher altltude to go hiking. My 2010 Prius has 77,000 miles.

Today, when going down a 5 mile hill stretch in the Mountains, the battery monitor on the dash stayed where it started, a couple of bars below the max, rather than topping up as usually happens during a long down hill.

I have a Scanguage which showed the battery state of charge remaining in a very narrow range around 60%. When I would periodically brake lightly to prevent the car from speeding up, the display of regenerative braking would stay at zero. It was like the computer thought the full S.O.C. is 60%. Some charging seemed to be happening because the level didn't go down, even when the road leveled off.

A while later, on another long down hill, everything returned to normal, S.O.C. got up to 80% (Full), the dash monitor went to the top and regen braking was active on the Scanguage.

Fuel economy was normal, near 50, for the day and the car drove normally throughout.

This same odd behavior happened once before, about a week ago, at similar altitude (8,000 to 11,000 feet), then returned to normal.

When we got home I checked the Scanguage for error codes. There were none.

So, could this be a sign of a battery problem, a problem somewhere else in the hybrid system or should I just ignore it? Anyone else experience something like this?

 

Good idea. On both occasions I had passengers in the back seats, might have been blocking the intake. In fact, battery behavior returned to normal after dropping off the passengers. Makes me think that I don't have a serious problem.

But I will check the grill and fan. I will also monitor the battery temp with the Scanguage.