Progress in battery technology is closely tied to that in electronics. The changes from vacuum tribes to transistors to micro circuits have resulted in major improvements in energy density, shelf life, and reliability of batteries. However progress is slow compared to advances in electronics circuits. Growth in new systems, once in production, is also slow, depending upon the development of new devices which need their performance characteristics. This has been true, in particular; for lithium cells operating at 3 V. Older electrochemical systems such as C-Zn, alkaline, Zn-Air, NiCd, and lead acid continue to get better, and maintain the market for devices which can use them. Primary lithium batteries ave growing in use as new devices are designed around their higher voltage and superior shelf life. The Li-MnO2 system dominates the commercial market. At least 16 manufacturers produce many sizes and configurations from high rate ''D'' cells to 50 mAh thin, flat cells. Two new secondary (rechargeable) systems, nickel-metal hydride and lithium ion, have recently been introduced. They are growing at a rapid rate in response to environmental concerns and the need for higher energy density. Other secondary systems such as Zn-air and lithium-polymer electrolyte are nearing commercial production. Environmental regulations continue to impact battery use and disposal, leading to more interest in secondary systems which can be reused many times before disposal. Mercury has largely been banned from use in primary batteries, both as a corrosion inhibitor for zinc and as a cathode in the mercuric oxide cell. Existing and emerging battery systems are discussed in terms of energy content shelf and cycle life and other characteristics. Energy density and cycle life, in particular are application dependent and will vary with discharge rate, duty cycle, and operating voltage of the device. This leads to some confusion in the literature, where a wide range of values can be found.
