Today mine (iPhone 5, iOS 7.0.3) showed about 60%, then the little 're-spring' circle of white dashes blinking, then dead. Press power button- and the 'plug it in; it's dead' screen showed. Plugged it in, turned it on and battery immediately showed 60% and started charging, too fast I might add..at least going by what the screen showed.
If we can't even have the "phone's best guess" be remotely accurate for battery drain, then why show it AT ALL? We should just always assume it has enough juice for only one text message, and carry a charger/solar panels everywhere.
This is ridiculous. Mine wasn't doing this before iOS 7, either.
I already emailed a local authorized Mac repair place, I'm going to make an appointment and see if they will replace the battery. Bought mine in February so it does have a warranty still.