Raspberry Pi power backup or UPS

A power failure on Raspberry Pi can be fatal for the SD card if the failure happens while data is written to the file system. In such case, not only the file system but even the SD card might be destroyed as reported on the internet.
power failure destroys SD card on Raspberry
I have spent some time and made a Raspberry Pi UPS with the following features:

• operation of Raspberry is continuous
• for longer power failures, the operating system shuts down
• operating system reboots if power comes back
• rechargeable lithium battery included and charging circuit is onboard

A full description can be found here:

Safe-Power for Raspberry PI

August 2015

 A version with updated firmware and redesigned PCB is now available.