Heheh this is a cool idea. Although on the top cylindrical battery, the vertical highlights at the top and bottom of the side of the battery make it look like it has a long edge there. I'd recommend either removing them or joining them up and making the ends straightened instead of curving into the ends.
Also, the eyes and lower battery share the same lightsource, but the upper battery has light coming from the front. With those lightsources, the shadow cast by him would extend backward behind him, if you went with ther frontal lightsource, or extanding slightly over to the right if you chose the upper-left lightsources. The lower battery would be partially cast in shadow if you went for that latter lighing.
Finally, the shading on the upper battery is clearly in strips and the dithering doesn't combat this much really. I recommend trying 25% dithering either side of the 50% dithering you already have. Either that or no dithering at all (that would probably look quite nice too).
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