I suggest you should check these things.

1) Program the chip so that the crystal frequency is buffered to the output pin. Then connect a very accurate frequency counter to this pin to see if the OSC frequency is changing. (Do not connect directly to the crystal. The meter connection will change the crystal rate).

2) Look at your diodes used for the power supply. You should use very low drop shottkey diodes for this. If you tried to use something like 1N4001 then the operating VCC of the RTC chip could be lower than the high levels of the SDA and SCL lines. Signal lines to chips that get too high above the Vcc can cause chip upset problems.

3) Search this forum for info on this chip. I have at times had problems with it. I fixed those problems by making sure that I read out all the time data using a multi-byte read sequence. The chip does some strange things when you try to read time bytes out individually with separate I2C transactions for each byte.

Michael Karas