Add a controller suited specifically for docking with some open standards on docks. Then add in a go-to-dock Bt node to go to a staging point and then enable the docking controller to dock the robot. This will allow autonomous docking with the is-charge-low BT node for a robot to go back home when it needs to.

The docking controller should work on a configuration of the dock shape, using april tags, or some other form of standardizable relative pose estimation for the docking controller to target an approach at a particular vector and end position.

https://datascience.stackexchange.com/questions/6838/when-to-use-random-forest-over-svm-and-vice-versa

Also offer a Bt with this built in (if charge < X, go to docking subtree. Once charge > Y, reenter navigation subtree)