Switching setup to reverse B2B charging direction
You can make your own DPDT switch:







simulate this circuit &ndash; Schematic created using CircuitLab

Or just use jumper-style cables, e.g.:


Cut it on the one side to allow quick swapping. Fixate with a bolt.
Takes a minute or so for each swapping, with little wear. High current capability, super low cost, full control over variables...

Have fun! :)