Rechargeable batteries have been designed for powering hearing aid devices (HAD). The cells, based on the lithium-ion chemistry, were designed in a size that is compatible with the existing HAD. The 10 mA h batteries were tested to characterize the design and the electrochemical performance from the point of view of a typical HAD application. Results are presented for constant-current tests, first-cycle conditions, charge voltage cut-off, rate performance, and cycle life. The pulse capabilities and the preliminary safety tests of the batteries will be presented in a following report. The results of the lithium-ion HAD cells developed in this project are compared with other battery chemistries: lithium-alloy and nickel–metal hydride secondary batteries and Zn–air primary batteries.