Hi Mohit,
I've been using a 3.6V (150mAH) backup battery for several years now on >75 products in the field - no failures yet.
Although I used a MAX691 to detect power fail and could have used the VCC/VBB switching feature, I ended up connecting the backup battery to VCC via a series resistor (Rcharge) to limit Icharge to 0.5mA. (Rcharge=(Vcc-3.6)/(0.5*10E-3)).
I also used a Schottky (for its low Vf) diode in parallel with Rcharge as you described.
Since the battery is almost always fully charged (ie>3.6V), Icharge is usually << 0.5mA)
Happy to provide further details if you wish

regards,
Allan Coyne