A different Battery Problem

Last night I looked at my iPhone before going to bed to see if I should charge it. The battery indicated it was full. I didn't think anything of it since I can go two days on a single charge if I haven't used it that much. Then today it was still full. Then I went to use it to make a call and it was turned off. I had to power up then it said no juice on battery and needed to charge. Odd?

I've had it say it was empty and it wouldn't let me power it on. I forgot to charge it overnight. I went to go try it the next morning and I could power it on.
I wouldn't think anything of it if it only happens once.
I suggest just a reset and charge it back up.
Bryan