Many different countries use different voltages for charging devices, where as a AA battery anywhere in the world would be compatible with your e-reader. (goodereader.com)
In an elegant and ingenious setup, the collaborations separately explored a nickel - oxide anode and a lithium - nickel - manganese - cobalt - oxide cathode — both notable for high capacity and cyclability — by placing samples inside common coin - cell batteries running under different voltages. (sciencedaily.com)
Here is a multi-tasker that defies logic; They use different voltages, the radio has to be insulated, it is just silly. (treehugger.com)