A 650 Farad / 2.7V ultracapacitor with an extremely low internal resistance of max 0.8 milliOhms from market leader Maxwell. This is a discontinued product but as they have been in storage since 2007 and have not seen any current nor high temperatures we found that they are in very good condition. Measured ESR is below spec (0.5 milliOhms typ) capacitance at 100% leakage current also in spec. The datasheet is available here.Their regular price was in the order of 50€. We are giving them away to DIYers as we could make a very price competitive acquisition of ~ 800 parts these are well suited to power a kWeld. Based on the measured cell characteristics 4S pack should delivery roughly 1600A welding current. If you need larger quantities of these, then please consider their original packaging of 30 pieces if possible.