If such AI decides that energy spent toward human agriculture (biological food that the AI does not need) is less important than work spent toward storage and production of energy (electricity that the AI needs), then why wouldn't it just try to re-direct resources from the former to the latter. And the AI is some sentient superintelligence, I think it is safe to assume that it will be able to outmaneuver human safeguards.
Obviously that is still just a very hypothetical sci-fi scenario, but the consequences could be very dramatic.