I take care of the equipment of 20 Sennheiser Kinnbügelhörer RR 820, which are gnutzt week. Their first battery held more than 5 years, then they had to be replaced. At first I tried "identical" batteries from other manufacturers. Although they were cheaper, fit well in the handset RR 820 but only by force in the Sennheiser charge strip, can be loaded simultaneously with the 10 batteries. So it had to be but the original batteries, and anyway, the price / performance ratio is really good when you consider how long the hold. The contact with the seller and the delivery were good.