Caps tend to explode when they fail, and high energy caps explode violently. You always, always, want to round down when spec'ing caps, not up. But forget all

Caps tend to explode when they fail, and high energy caps explode violently. You always, always, want to round down when spec'ing caps, not up. But forget all that. Lets do it differently and fix our math toward the author's original comparison, the 1500mAh battery, not his weird, somewhat arbitrary choice, of a 6V-rated cap which drains to 2.5V after ~10 hours. And instead of talking about electricity, let's talk about what we're really after: energy. A 1.5Ah battery stores about 22.68kJ of energy when fully charged to 4.2V (1.5Ah×3600C×4.2V=22,680J). From above, At 2.7V, a 1200F cap stores 8.478KJ of energy. 22.68kJ/8.478kJ = 2.675. Meaning we need at least 3 of these caps to meet or exceed the energy storage of a 1500mAh battery. So we're both wrong in the context of the original comparison. And more importantly, so is the author. Edit: This 3000F supercap rated for 2.7V would get us damn close to the 22.68kJ requirement, coming in at 21.87kJ of total storage: http://www.mouser.com/ProductDetail/Maxwell-Technologies/BCAP3000-P270-K04/?qs=sGAEpiMZZMuDCPMZUZ%252bYl4vDGR228uRDhgVZbUDv3h0%3d http://www.mouser.com/ProductDetail/Maxwell-Technologies/BCA... Edit again: I messed up again! The battery energy capacity is actually less than 22.68kJ, because the energy equation I used assumes that the voltage stays constant during the battery's discharge cycle. It doesn't. For a constant-current discharge of a LiPoly battery, the mean voltage is something like 3.4-3.6V (estimating from the discharge voltage curve, assuming discharge stops at 2.7V). So really we're talking something closer to 19kJ of energy stored within the battery. By the figures in her submission, her cap would weigh 262.6g and would occupy 30.8m^2 (no figures on thickness to calculate volume). Titanium density is 4.5g/cm^3. Assuming titanium dominates the density of her material, it'd be about 58cm^3 in volume - something like 10cm by 5.8cm by 1cm. If the density matched that of copper, it'd be about half that size.