BitChar-G battery cells are not commercial cells (meaning they do not have industry standard dimensions) like A, AA, AAA etc. This is why you cant and wont find them in your local electronics shop. They are industrial cells, used for specialty applications, usually for OEM or industrial purposes. There are only a handful of industry manufacturers who make the size, but the dimensions vary by manufacturer by +/- 1 or 2 millimeters, because there is no set dimension standards.
This cell is available by buying a BitRacer, and taking the battery, or buying a cheap clone and doing the same. you can also go to
QuestForMadness.com and buy one online for $3.