Clearblue Ovulation Kit Question

So I've had 4 days of blinking smiley faces. Tonight I started cramping and getting bloated so I took another one and finally got my solid smiley face. BUT...it hasn't left the screen and it's been an hour. So now I'm wondering if it was faulty or if the battery was going. I'll take another one in the morning with a new holder but I'm curious if anyone has had this happen to them???