Combine solar cells with a rechargeable battery and you get Knut Karlsen’s SunCat Battery–1.8 volt thin-film, flexible, photovoltaic cells wrapped around a 1.5 volt NiMH battery with a conductive silver pen and flat wires.
The SunCat, still in the prototype stage, completely removes the need for chargers since the battery can charge itself. Karlsen’s device is similar to a solar trickle charger, which slowly juices up batteries over time while never overcharging them. The inventor speculates that a second version of the SunCat could have capacitors attached to charge it more efficiently.
While the SunCat could be useful in emergency situations, it probably won’t become a mainstream hit–photovoltaic cells permanently attached to electronic devices are much easier to keep track of than batteries.