Actually there is a new brand of "ultra-capacitors" out there which are electro-chemical instead of simply holding static-electricity. The problem is that they're way too expensive at the moment because they are a new technology. They can discharge really fast like capacitors but they hold way more energy than convertionnal static capacitors. In essence... they are a cross between a capacitor and a battery. Do a search on the web and look for either "ultra-capacitors", "super-capacitors" or electro-chemical capacitors". Just my 2 cents.