Flash's battery is not intended to be removed or replaced by the rider.
This is really a matter of preference in design. We understand that some riders prefer to be able to swap out batteries. However, we prefer a simpler experience for most riders who want to simply plug the bike in without having to remove the battery.
Additionally, by not bolting the battery onto the frame or designing a special system for swapping batteries, we save on cost and weight, allowing us to provide what we think is a better product at the most affordable price possible.
Visually, the internal design also gives us a cleaner, purpose-built look that we love.