Rabbit 2000 not keeping correct time


I have a problem with a program I have running on a rabbit 2000 cpu. When I upload my program the date and time is correct but when I leave my program running for a long time the clock seems a little bit too slow.

In about 48 hours I loose about 2 hours on the clock.

What can be done to improve that, syncing with an NTP server periodically is not possible on this project.