Best thing to do is to use the Official BlackBerry Travel Charger included with your 9700. The worst thing to do is to use a "powered USB socket" type charger of the LOW-OUTPUT/LOW VOLTAGE variety, as they don't provide enough juice to charge the 9700. Let me explain further.
I own this model of Belkin Travel Surge Protector...
...which I use when I'm, surprise, surprise, traveling! As you can see, it gives 3 surge-protected outlets, plus 2 powered USB ports, into which you can plug USB cables for charging your cell phone, Bluetooth headset, MP3 player, Nook or other eBook reader, etc, etc. The idea being to leave your bulky chargers at home, and just use this as the charger for 2 devices, which I was able to do perfectly fine with my old Curve 8900, and also with my fiancée's 8530 Curve. Plug in a micro-USB B cord into the surge protector, plug the micro end into the BB, and it would charge... until the 9700. When I tried it with this phone, I got an on-screen message saying that the charger did not provide enough power to charge my phone!
That's when I found out that there are LOW-OUTPUT and HIGH-OUTPUT models of powered USB ports. Belkin needs to make an updated model with HIGH-OUTPUT ports, that would solve the problem. Until then, I still have to carry & use the travel charger that came with my phone, even though other models of BlackBerry have no issue with the low-output powered USB ports.