I ended up misreading this as sort of "Well I don't know if it's a clock, that's why I need the batteries to find out" and found that reasoning to be funnier than the pun which flew over my head initially, simply for being such a comedically unconventional, yet entirely possible situation with several implications that could be made, such as just assuming something must be a clock, and immediately wanting to try using it as such, even though it might not actually be a clock.

Now if only I had something to measure my disappointment like a clock measures time...