Agree, the L828/A27 battery type is a bit unusual but can be found online quite easily. Also, the remote itself is a bit clunky and I saw reports that mentioned to have issues with water/sweat ingress as it is not waterproofed. Just in case, I wrapped it in a small plastic bag which sits nice in the included holder.
First indoor session yesterday was a 30min FTP test - I don't think I would have been able without it; totally needed that setting 3 at the end