The pocket warmer "eneloop kairo," from Sanyo is equipped with a Li-ion rechargeable battery. When the warmer is connected to a dedicated AC adapter and charged from an AC power source, it can repeatedly be used about 500 times. The warmer takes about five hours to charge.

Sanyo pocket warmer eneloop kairo measures 84 x 62 x 19 mm, weighs about 85 g. and will be available from December 1st 2006 for approximately 4,000 Yen ($35).
Via Sanyo (Japanese)