If the battery is drained, you should be able to remove it from the bottom of the grip. It looks like that model of camera uses an LP-E6 battery to run most of the camera features. Canon has them for around $100 if you can't get that one to hold a charge. You can also search the battery model in your browser and find less expensive alternatives. I have attached a link to a user manual for this model of camera if you need guidance on the battery location.
https://www.bhphotovideo.com/lit_files/42005.pdf
There is also a guide on Ifixit, that I have linked below, on replacing the button-cell battery that stores the date and time. It is a relatively simple procedure.
[guide|55588]