A vast majority of the two way radios that we sell come standard with rechargeable batteries. These rechargeable batteries fall into three categories (NiCd, NiMH, Lithium), and we are often asked to explain the difference.
I recently found some information on Motorola's web site that does a great job of explaining the difference. This page also provides links to material safety data sheets (MSDSs) for Motorola batteries, and battery recycling and safety information.
Here's an excerpt that discusses the differences:
Motorola makes many different models of batteries, with the majority of them falling into three major types: Nickel-Cadmium (Ni-Cd), Nickel-Metal Hydride (NiMH), and Lithium Ion (Li-Ion).
Motorola Nickel Cadmium (NiCd) batteries are currently one of the most cost effective chemistries on the market. NiCd batteries give you more watt-hours of operation per shift than other battery chemistries. They are ideal for a user who needs a high-performance battery and who communicates under extreme conditions of cold and heat (-30C to +50C) Historically, a NiCd battery's major drawback has been its susceptibility to memory effect, or its propensity to "forget" and not utilize its full capacity. Today, this remains to be a serious tradeoff, but can be minimized with proper charging/reconditioning practices.
Motorola Nickel Metal Hydride (NiMH) batteries can offer superior operation life between charges. This battery chemistry provides 30-40% longer operation time than NiCd, but does not operate as efficiently in extreme temperatures. In addition, NiMH is less susceptible to "memory effect" compared to NiCd batteries.
One of the major advantages of Motorola Lithium Ion (Li Ion) batteries is their power to weight ratio, which easily exceeds that of NiMH for a lighter, smaller power supply. These batteries tend to be the industry's most expensive chemistry, and they offer a major advantage of not experiencing "memory effect".