If you want to build a good Real Time Clock for your Raspberry here’s the tutorial you were looking for!
This is a revised and simplified version for Instructables made out of this article at my personal blog. Difference is mainly in the structure and my article is a bit more verbose.
Why another “annoying” how to on building a Real Time Clock for the RPi?
Because almost everywhere you find instructions telling you to build the circuit on a breadboard and simply wire it with a couple of loose wires.
This is a full Stacking Shield you can elegantly install on top the RPi leaving the GPIO entirely exposed for other devices. And you can build it for no more than 8$, instead of buying one for double the price.