Competitive Battery Technologies
To satisfy the power requirements of a handheld PC device [HPC], there are three vanguard cell chemistries that are available to the designer, Nickel-based systems such as Nickel-Metal Hydride, Lithium-based, Lithium-Ion, and Alkaline cells in both primary and secondary [rechargeable] formats.

Nickel-Metal Hydride [NiMH]
With an energy density nearly twice that of its Nickel Cadmium [NiCd] counterpart, NiMH cells offer designers the ability to double the usage time of a device over a NiCd powered product. Like NiCd, the NiMH cells are a 1.2 Volt per cell system with a very similar internal impedance profile. With its stable voltage profile, decent pulse-rate current drain capability, and its acceptance of quick recharge regimes [up to a 3C rate], NiMH cells are one of the leading choices for portable and handheld products.

Unlike NiCd batteries, the NiMH chemistry does not suffer from the memory effect condition. This nemesis of NiCd cells is brought about by repetitive shallow discharge cycles of cells in an application, rather than full, complete discharges to the cell's 1.0 Volt endpoint.

NiMH cells perform well in applications where the use and duty cycle of the device is well understood and predictable, combined with a medium to high frequency of use. For example, a cellular phone powered by NiMH and used regularly as a business tool, extends the user's talk and standby time significantly over a comparable NiCd battery pack. However, because of its high self-discharge rate, about three percent per day, an infrequent user of a cellular phone with a NiMH battery can be plagued with short battery life unless they remember to recharge the batteries prior to use.

Lithium-Ion
The Lithium-Ion [Li-Ion] battery is a relatively high energy density rechargeable system which allows designers to reduce the form factors of their product. Depending on the amount of battery capacity required for the application, the size of the device can be reduced dramatically using this chemistry as the power source.

Unlike metallic Lithium cells, Li-Ion keeps the Lithium in an Ionic state. Metallic lithium is very volatile and reactive, to the point of burning in the presence of water. Lithium Ion cells retain the electrochemical properties of a Lithium cell [i.e. Voltage profile] while eliminating the inherent safety issues associated with metallic Lithium.

Li-Ion cells, also known as rocking chair technology [RCT] because of the way the ions are shuttled back and forth between the charge and discharge function, relies on intercalation of the Lithium Ions into the active material on charge and de-intercalation during discharge. From a design standpoint, the nominal 3.6 Volts of this Lithium system can reduce the overall size and weight of the battery portion of the device.

Primary Alkaline
Given the wide array of battery options available to product design teams, primary alkaline batteries are still one of the dominant power systems chosen for portable, handheld devices, be it an electronic entertainment product or a productivity tool like a handheld PC.

The clear advantage of using primary alkaline cells is reliability -- the power is there when you need it -- no concerns about shelf-life; no concerns about retail availability of replacement cells. The big drawback can be cost, especially if you're a heavy user of a power hungry device.

Rechargeable Alkaline
The discharge capacity of rechargeable alkaline cells fades with each cycle, with the majority of the fade occurring in early cycles. (After about 10 cycles, they're no better than NiCd!)

These characteristics make the rechargeable alkaline system ideal for intermittent-use and/or frequent-recharge applications. Ideal applications for rechargeable alkalines include low- and moderate-power portable applications such as HPCs. cordless phones, CDMA phones, or portable terminals.