DS1338C-33 - Dallas Semi. RTC w/ 56byte NVRAM & Internal Crystal 3.3v
In order to add a RTC to your zipit you have to do some very delicate soldering. If you don't have a ultrafine tip iron, and a few years soldering experience - do NOT attempt this. You will be soldering wires directly to the LPC915, if this chip is damaged your zipit will not boot.
Connections to Power
You have two choices for battery backup of the RTC, running off the ZipIt's rechargable (bad idea, clock isnt happy with the full range of the battery), or adding a coin battery just for the clock. Originally I attempted to run the clock backup feed off the ZipIt battery only to have trouble with the clock dumping randomly. I now use a 3.3V coin cell harvested from a dead Playstation2 with no problems.