HI,
this is exactly what I have (except I used a normal diode), I also added a 220kohm resistor in series with the diode to keep current down. Higher then that for the resistor, the RTC would not keepa good time. The problem I am facing now Is that at the begining I had 3.09volt, its decreasing by 0.01volt everyday, Its been almost four days now and it is at 3.05volt, at this rate the battery wont last more then a few weeks... my casio wrist watch battery lasts about 4 years.... !!! and thats including the display on all that time !!