Kelly, a Google search says you’re right. It needs to back to Canon as it’s not a user replaceable item ☹
I did find this which may or may not help.
Good luck!
Built-in Rechargeable Lithium Battery
The camcorder has a built-in rechargeable lithium batteryÂ
to keep the date/time and other settings. The built-inÂ
lithium battery is recharged while you use the camcorder; however, it will discharge completely if you do not useÂ
the camcorder for about 3 months.
To recharge the built-in lithium battery:
Connect the DC cable and compac
t power adapter to the camcorderÂ
and use a household power outlet to power the cam
corder for 24 hours while it is turned off.”
This means that an authorized Canon service center will have to replace it. I don’t know of anyone who sells this battery or where you would get instructions on where it is and how to change it. You will need to send your camera to a country that has an authorized EOS Cinema camera repair center.