With that in mind, Panasonic has just announced its CG-320. Measuring 20 x 3.5 mm, it's being billed as "the industry's smallest cylindrical shaped rechargeable Lithium Ion battery."
The CG-320 weighs 0.6 grams, has a nominal capacity of 13 mAh, a nominal voltage of 3.75 volts, and a maximum charging voltage of 4.2 volts. It also has a stainless steel exterior case, designed to prevent swelling.
The battery incorporates the same spiral electrode construction as used in regular cylindrical Li-ion batteries. This allows for a relatively wide area between the anode and cathode, which in turn results in high output for its size – enough to power near-field communications (NFC) systems, which will be one of its main applications.