Hello and sorry you're having problems. The 9 volt battery for the display on the bars of the bicycle goes in underneath the display (on the bottom of it).
You can also see the 7th page (pages are not numbered, simply scroll to the 2nd to last page) of the manual at the link below to see where the battery installs:
If you need further assistance let me know. Please do not forget to click at least a 3 STAR RATING, at the top of the page for my efforts.
Did you look at the manual I posted above?
Okay, digging deeper here.....
Yes that manual I posted states specifically it is for the C9i. The following manual ALSO states it's for the C9i (shown on the first page of the manual). Look at that page and view specifically where they show the 9 volt battery:
On the cover of that manual it states: "C9i, C7i Exercise Bikes Assembly Instructions".
The 5th page in shows the exploded view of the bike. It also shows only ONE battery (a 9 volt) and shows it's location. Are you able to see that on the page of the manual? If so, are you saying your C9i is different than the C9i they show?