Yesterday I got my Stalker and started some tests. I powered the Stalker through the VCC/GND pins of the program port, using a USB/TTL cable. I mounted a backup battery (CR2032) on the board.
Using the DS1307RTC and Time libraries, I set the RTC clock to my laptop’s clock, and everything worked as expected. I set 10 seconds as the sync interval in the Time library.
However, after a few minutes I noticed that the RTC on the Stalker lost a few seconds with respect to my laptop (which is kept in sync with NTP). I haven’t calculated an exact figure, but the Stalker seems to loose several seconds every few minutes.
The software clock provided by Time [ now() ] and the RTC’s one [ RTC.get() ] agree, so the two are in sync. It indeed seems that the RTC chip is loosing time, much much more than the few PPM tolerance per month that the Maxim’s chip advertises.
Is it possible that my board got a defective DS1307, or am I doing something wrong?