The Lithiums make great spare batteries since they have about a 10-year shelf life. They cost about four times the price of alkalines, and last only about three times longer. NiCd batteries are more readily available but have the lowest capacity of any of the types discussed here. NiMH have higher capacity, but not all Handheld PCs recommend using them. Battery life To understand battery life, you need to know some characteristic parameters of batteries.
Voltage is the parameter that is the most used, and the most misunderstood.
Alkaline AA batteries start out with a voltage of about 1.5 volts per cell, or a total of 3.0 volts. Alkalines are unique in that their voltage drops at a slow and relatively regular rate as you use them. Knowing this rate and the present voltage of the battery makes it possible to determine remaining power. Handheld PCs have built-in hardware to measure the voltage of the batteries, as well as the software to estimate the remaining power of the batteries. Rechargeable batteries start out at around 1.2 to 1.4 volts each, or 2.4 to 2.8 for a pair.