It's the same, except it has a built in battery and is rechargeable with a lightning cable (which the port is located on the bottom of the device, so you can't use it whilst charging).
When mine dies it’s a good excuse to find a cup of coffee. By the time I get back there’s more than enough charge for the rest of the day.
[1] http://batteryuniversity.com/learn/article/how_to_charge_whe...