i just bought an aftermarket undertail and i have no idea where to mount the battery. it eliminates the undertray so i am stuck on this one....

 

My guess is you have an 99 F4. Just follow this link and it will show you how to do the undertail install. Yes I know it is for an F4i, but it is for a newer model F4i which is almost the same as the F4. I used these instructions to do my undertail install.

https://cbrforum.com/m_154971/tm.htm