[@The Jest] Well first of all, he'd only be able to drain from one target at a time (may change later on as he gains experience). The rate of said drain wouldn't be enough to make someone pass out within seconds,  more so make a target more fatigued & sluggish. (again, may change with time / experience) Furthermore, he'd only be able to handle so much built-up energy in himself at a time. The energy drained would not be able to change forms (i.e electrical to chemical to kinetic) at least at the start. He'd also need to be careful to not "overcharge" someone / something or risk damage to said person or thing.

EDIT: Why did I think it would be a good idea to write this out on mobile?!