I got one of these quads from a friend. The only thing is the remote does not have a battey and there is no information anywhere to tell me what size battery the remote itself takes. Shorter then a AAA, but about the same diameter. Can anybody open their remote and let me know what it takes?

 

i apologize as i do not have a remote. but have you contacted Eton for the information?
if this is the part, you may call these folks, surely they'll give you the answer.

Fig 11: Remote Control Assembly

Anything ATV - RXL40E - Viper Jr Electric Start