Has anyone else experience this?
No.
Your battery is probably on the blink
I would first suggest that you restore your iPhone through iTunes.
If you continue to experience the same problem, take it to apple because your iPhone may have come with a bad battery
I did do that and it still did the "charge battery" screen after being halfway full with no notice.
bring it back and get a new one
update: Iphone is going at 8hrs 40 minutes usage time, and 1 day 7 hours stand by time and its about 3/4 full.
is that a good standard?
Amazing standard. I get no where near that, congrats!