While you can't whittle yourself a battery, how about a rechargeable battery made with wooden anodes? What always intrigues me about discoveries like these is not even necessarily the end result, but how the idea came about - where do "wood" and "rechargeable battery" meet in a person's mind? Apparently, the fibrous nature of wood, and it's ability to soak up liquid electrolytes make it an environmentally friendly material suitable for a long-lasting rechargeable device.
KurzweilAI“Existing batteries are often created on stiff anode bases, which are too brittle to withstand the swelling and shrinking that happens as electrons are stored in the battery and used up. The scientists found that wood fibers are supple enough to let their sodium-ion battery last more than 400 charging cycles, which puts it among the longest-lasting nanobatteries.”