change in energy bar fluctuation

I have been experiencing alot of energy bar fluctuation lately. I live in the desert, and so i drive on relatively flat ground, with an occasional trip to the mountains. Even in town, i can start with 5 blue bars, then go up to 1 or 2 green bars, and then after 10 minutes or so of driving it goes down to 2 pink bars. On a trip to the mountains, i started with 6 blue bars, then got up to two green bars, and then went down to 2 pink bars, all within a matter of 30 minutes. Sometimes i will park the car and the monitor shows 6 blue bars, or even one green bar, and an hour later i return and when i start the car and drive for a few minutes, the monitor goes down to 2 pink bars. The car has always replenished the bars, but the monitor didn't used to have some quick fluctuations. Anyone else experience this?