An Irish photographer David Hunt has been named one of the small connecting Raspberry Pi to a battery of a digital SLR (DSLR) Canon D5 Mark II, and then uses that device to transfer captured photos directly to an iPad.
In his explanatory post, the minicomputer running a small Perl script that monitors if they are taking new pictures in the camera, after which the application sends the call Shuttersnitch iPad via the Internet.
User has posted a video where you can see how this process through an Ethernet cable, but get the same functionality with WiFi is also possible. Others possibilities of connecting the Raspberry Pi to these external batteries is to safeguard the photos on a USB key or an external hard drive, or have a full remote control through WiFi connectivity.