Energy density is the most significant factor in secondary (rechargeable)consideration, but other important attributes are service life, load characteristics, maintenance requirements, self-discharge and operational costs.
–Nickel-cadmium – (NiCd) mature but has moderate energy density. Nickel-cadmium is used where long life, high discharge rate and extended temperature range is important. Main applications are two-way radios, biomedical equipment and power tools. Environmental considerations are also important in this category, as nickel-cadmium contains toxic metals that must be disposed of properly.
-Nickel-metal-hydride (NiMH)- has a higher energy density compared to nickel-cadmium at the expense of reduced cycle life. There are no toxic metals. Applications include mobile phones and laptop computers.
-nanotech processed electrode provide x5 more power and x10 longer cycle life at 20% of the weight.
- -ion-polymer – Similar to lithium-ion, this system enables slim geometry and simple packaging at the expense of higher cost per watt/hours. Main applications are cell phones.