How did you take off the battery? The glue is so strong, I was afraid of puncturing the big lithium battery pouch when I was attempting to take the battery out.
I did not, it is still in its original case. In the new case there is a holder for a cylindrical li-ion battery. Have not dared trying it yet, though, but pretty sure it will work.
Have a K3 Pro at work, and I think the K8 Pro feels a lot better, especially with the 3d printed case. Because of the reduced travel I keep bottoming out the keys on the K3 which does not feel like it is good for my hands. Also tried o-rings, but they don't work the same way as on a normal profile keyboard.
The V-series is a lot lower, and if I knew about those from the start I'd most probably just get one of those and skip the bluetooth.