Battery charger ICs are integrated circuits (IC) that are used to charge batteries. There are several types of battery charger ICs. Linear chargers use a voltage-controlled source to force a fixed voltage to appear at the output terminal. Switching chargers use an inductor, transformer, or capacitor to transfer energy from the input to the battery in discrete packets. Some battery charger ICs are designed to charge lithium (Li) ion or lead acid batteries. Others are suitable for charging nickel-cadmium (NiCd) or nickel-metal-hydride (NiMH) batteries. Important features for battery charger ICs include over-voltage protection and over-current protection. Devices with a soft-start feature condition the battery for several minutes before performing a fast charge. Devices with a charge status indicator have a built-in monitor that displays the amount of current supplied and/or the amount of charge applied. In response to concerns about the environmental impact of using lead (Pb) in solder finishes, some battery  charger ICs do not contain lead in any form.