The caveat to be concerned is thermal management. I haven't watched that particular video but make sure you understand how the thermal management & safety aspects work. Lots of adapters bypass these or use unregulated batteries. Best case scenario in these situations the battery will run do low that it bricks & is unrecoverable. Worst case can result in fires & such. It can be done as evidenced by an adapter I made to adapt my 20v DeWalt batteries to an older 18v B&D weed eater I got tired of rebuilding the old Ni-Cad packs on.