These suckers are just like those on an octopus’ tentacles, just not as tasty – hence the name. The battery pack connects to the dock-port via a flexible cable, and takes around three hours to fully transfer its load of electricity into the iPhone. One juiced, the iPhone will be at roughly half-power, able to play video for 10-hours or offer four hours of talk time. The Octopus itself charges via a USB-cable.
Why use this instead of a combo case and battery? Because it only needs to be used in emergencies. Those battery cases add bulk to what is a pretty slim and pocketable device, whereas an emergency battery can be kept out of the way in a bag until needed.
The Octopus is pretty cheap, too, coming in at a shade under $30.
Source: wired