As you remember, Kendall is broken after Season 1 finale. He wanted to gain some kind of control and power in his life.

>  i think it was a display of kendall feeling absolutely powerless. he
> didn’t want to shut down vaulter, he did it “because his dad told him
> to.” he’s firmly under his dad’s thumb and hates it. he stole the
> batteries so he could feel some semblance of control in his life
> again, some modicum of power, however small.
> 
> – u/justsomehandsomeguy