Rapid development and miniaturization of portable and wearable electronics requires compact powering devices with highest possible energy density combined with mechanical flexibility. Energy density of Li-ion batteries can be increased by removing electrochemically inactive components such as metal collector foils, binder, and additives. We developed novel self-standing collector-, additive-, and binder-free electrodes fabricated by dry mixing of battery active materials with as- grown carbon nanotubes using a proprietary technology. Resulting composite sheets consist of the active material particles embedded in a 3-dimentional network of pristine single walled carbon nanotubes, and can be up to 2 mm thick (up 250 mg/cm2 of the active material, >35 mAh/cm2 areal capacity density in case of NMC 5:2:3). Various active material powders can be used in this technology. The sheets are very flexible and 10-15% stretchable. Due to their high electrical conductivity (103-4 S/m), free-standing electrodes manufactured from the sheets allow elimination of traditional current collector foils (copper for anode and aluminum for cathode) from battery architecture. The resulting bendable, twistable, rollable and foldable Li-ion rechargeable pouch cell batteries approach the ceiling of gravimetric energy density imposed by the lithium storage material. Using this novel battery architecture, we developed several prototypes of flexible batteries capable of powering various wearable electronic devices, including a wristband-shaped battery that powers a commercial smart watch with heart rate monitoring and wireless data transferring features.