Android Question Android phone power bars turns red!

[Beja]

This is the first time.
* Power is 85% (no problem)
* Signal strength is all bars (no problem)

The problem is every now and then (2 to 5 seconds apart) some of the bars turns read or orange. sometimes the middle bars and another time the lower bars.

Any explanation.

p.s.
I noticed this only today after installing the finger print example application.