a different approach to installing the 51r battery (youtubes vid)
 

how i installed the 51r (seamlessly) by trimming the airbox:

Thanks for the post, this helped me install the 51R in my 2010 Fit Sport without cable extensions or modifying the tray. I only removed the 2 fins to the rear and took off the lower lip. The battery sits slightly cocked but no problem. I probably need to remove the battery in order to get the airbox cover off in the future though.