I have two DS1307 I2C RTC Modules
I hooked up the rtc to the mega and loaded the TimeRTCSet example from the Time examples
the sketch reports the time as 0:00:00 1 1 2000. I sent the command T1353540094 which is a valid unix time and the sketch starts reporting
23:20:00 21-11-2012 ... Ok seems fine. I hit the reset button on the arduino and the sketch resets and the time is still valid. I unplug the mega from the usb, plug it back in and start the serial monitor and the date defaults back to 0:00:00 1 1 2000. I checked the battery and it has 3.93v, I checked to see if the rtc was actually talking on the i2c bus by adding a Serial.println(RTC.get()); to the main loop and I get incremented time as I would expect. I disconnected the rtc from the arduion and the sketch stops so I can assume communications are working properly. I do have 10k pull resistors installed on sda and scl as tutorials have shown.
I asked the guys in irc and one of them said that if I didnt see voltage on the VCC / GND pins then the battery wasnt working, and I thought that there would be some kind of mechanism to prevent voltage/current flow from the battery to the vcc pin, dont know what to think...
Any help would be appreciated