Kind of. That is, the Riva is 750 mAh, while the basic* eGO is 650 mAh. However they are the same physical size. Although the price for each model varies from supplier to supplier (and from time to time because of sales), you are likely to find a Riva for a lower price than an eGO. Also the manual switch button on the Riva is a bit smoother than the eGO's.
* There also are 900 mAh and 1000 mAh Mega
batteries for the eGO (aka Tornado). They are longer, of course, especially the 1000 mAh Tornado version (from Totally Wicked).
FYI: There are other eGO-type models as well, e.g., the Hello 016,
Inferno, and
Vgo. [NOTE: The Vgo link is to just one of several suppliers which carry it.]
I say more about the eGO/Tornado, Riva, and Hello 016 on the bottom of
this page of my WWV
V2, with links to suppliers
here.