As you say, the α7R does not come with an external battery charger, you must instead use an external charger for the battery in the grip (one or two? I don't know). Charging over USB, may be required for the internal battery but will be very slow, so the grip with an external charger is a good move. Apparently Sony' charger is very expensive. However there are third party batteries and chargers available from places like Henry's or B&W in New York that may work and save you a lot of money. If you go this route, verify at Henry's that they do in fact work.
Sony A7, A850, A77, A700 || Sony>> 70-300G, 28-75 f2.8 SAM, 16-80CZ, 50 f1.4, FE 28-70 OSS, FE 24-70CZ f4 OSS, LA-EA4 || Minolta>> 300 f4 G HS, 200 f2.8 G HS, 100 f2.8 (D) Macro, 50 f1.7, 28 f2.8, 28-135 f4-4.5, 70-210 f4, 500 f8 Reflex, TC x 1.4 HS, TC x 2 HS. || Sigma 21-35 f3.5-4.2. || Tamron SP 24-135.