Is there any way to tell when the battery is fully charged? The green LED on the power button only indicates that the battery has "at least 20% power."
The only way I know to tell the state of charge would be to log into the devices web interface. At the top of the page on the right side, you will see a battery indicator that will show the state of charge. If it's plugged in and charging, the indicator will also show that by scrolling the state of charge bars. If it's not plugged in, it just shows how charged the battery is.
To log into the device, once you are connected by wifi, go to 192.168.1.1 and give it the same password you used to enable the connection. It's printed on the label under the back battery cover if you don't know it.
Mine constantly has the green light on and always shows that it is charging, even when it has been hooked to the AC adaptor for hours. I'm not sure the software interface is that reliable.