Although RIM do make an official desktop charger for the BlackBerry 9700 they do not make one which allows for syncing the BlackBerry and charging a spare battery.
Synchronize and recharge your BlackBerry Bold 9700 with the USB Sync and 2nd Battery Charge Cradle. The USB Docking Cradle holds your BlackBerry Bold 9700 at a comfortable reading angle and provides convenient access on your desk. With this device, you can charge your second battery and your phone at the same time. Charge and synchronize data simultaneously when connected to your PC. You can either use the included Mini-USB cable or the AC adapter connected to the cradle to sync and charge your BlackBerry Bold 9700.