I plugged my OS-2 into my Valve King 112 on the clean channel. Bypassed, i got no sound. Engaged, all I got was an intense high-pitch whine. Should I have tried a new battery?

Or is something else wrong?
Try a new batter before you do anything, and double check that you have your input and output right! may seem silly but ive accidentally done that without a clue whats wrong

But the battery may be (most likely is) dead, ive had similar issues there too.
Ball Custom Mark I

Korg Pitchblack > Dunlop Crybaby wah > mODDball audio Green Bastard > Marshall GV2 Guv'nor Plus > EHX Holy Stain > MXR Phase 90 > MXR Carbon Copy

Jet City JCA20h
Epiphone Valve Jr.
Blackstar HTV212
i agree, it might sound stupid, but one time i actually mixed up my ins and outs and the same thing happened