This is a high-performance replacement cordless battery for the Plantronics 66278-01, guaranteed to meet or exceed the OEM specifications of your original. The cordless battery is 0.86 x 0.45 x 0.252 inches with an output of 3.7 volts. The chemistry is LI-POL at 120mAH capacity. Manufactured by Empire Scientific, model number CPP-539. We offer a 1 Year Warranty with purchase. See this product elsewhere at a lower price? Call or email us; we have a Price Match Guarantee.