They explicitly state the top input module has to be changed to support the new battery in the video here

https://frame.work/ca/en/laptop13pro?tab=upgrade-to-pro

Unless you can put the old battery in the new bottom panel, you have to upgrade all 4 at once if you upgrade the bottom

They also said you need the new touchpad and top plate to have enough clearance for the battery

Bottom panel, input panel, battery, and speakers have to be all pro together

You can put the new input panel on the old bottom panel, though

V8.40 => V8.40 🤔