I recently purchased the Canon Rebel T6 kit with 18-55mm lens and the 
Canon Custom Accessory Pack, which included a lens cleaning kit, a UV 
filter and 2 3V Lithium CR2 batteries.
I have read the blog:
https://www.apogeeweb.net/electron/cr2-battery-basics-replacement-and-safety-precautions-faq.html

I have never seen this size battery before. Can anyone tell me what 
they're used for?
thanks in advance