How long has Data been isolated from Federation-like power sources? His head was stuck underground for centuries, but I assume he used his suspend-to-disk feature. Or his head could have a small radioisotope generator that provides just enough power to keep his brain intact.
If separated from power sources for an extended period of time, Data holds his arms out and harvests wind energy.
If separated from power sources for an extended period of time, Data holds his arms out and harvests wind energy.