Is it safe to charge a supercapacitor from a source with more than it's rated voltage, provided that the voltage across the cap never exceeds the rating? For example, the cap is rated at 2.7V, and i charge it from two AA batteries giving just over 3.2V in open circuit. Once the battery, which gives vastly less current than the cap can draw, is connected to the empty cap, the voltage across it stays near zero, and is slowly climbing. What i can't figure out - is the "never-to-exceed" limit of 2.7V apply to the voltage across the cap, or the voltage of the source that charges it? In the example above, the first is true, but the second is not. How does it actually work?