Battery chargers are used to recharge batteries which, after discharge, can be restored to a fully-charged state. Rechargeable batteries or secondary cells differ in terms of design and chemistry. Iron electrode batteries feature good energy density and low self-discharge, but have a low efficiency and provide poor low-temperature performance. They are more expensive than lead acid batteries, a type of rechargeable battery that accounts for almost 60% of all batteries sold worldwide. Battery chargers for lithium batteries are designed to support backup power sources for electronic equipment. When the battery is charged, lithium ions are driven from the cathode into the anode; when the charge is removed, the lithium ions flows back to the cathode. Other types of rechargeable batteries include metal or air batteries, nickel-cadmium or Ni-Cd batteries, and batteries that use chemistries such as nickel-hydrogen (Ni-H₂ ), nickel-metal hydride (NiMH), nickel-zinc (Ni-Zn), and silver oxide (AgO). Rechargeable zinc, alkaline, and manganese dioxide batteries are good low-cost alternatives, but their useful capacity is only about two-thirds that of primary cells. Battery chargers for these products are commonly available.

Battery chargers can be supplied by an alternating current (AC) power source or a direct current (DC) power source. Specifications for battery chargers include input voltage, charging current, output voltage, and operating temperature. Smart chargers are used to stop the charging cycle automatically when a rechargeable battery is fully-charged. Display type and cell size are important parameters for industrial battery chargers. There are three main display types: analog, digital, and LED. Often, light emitting diodes (LED) are used in segmented or dot matrix displays that provide numeric or alphanumeric representation. Cell sizes for rechargeable batteries vary widely. Standard battery types include AAAA, AAA, and N; AA, 1/3 AA, 2/3 AA, and 1/2 AA; A and 2/3 A; C, Cs, and 4/5 Cs; D and 1/2 D. Each of these styles is cylindrical, with a positive top that has an extended terminal; and a negative, slightly indented bottom. 9-volt (9V) batteries are also a standard battery type, but they are rectangular with extended positive and negative terminals on their tops. Nonstandard rechargeable batteries include: prismatic cells, coin or button cells, sachet cells, lantern batteries, and battery packs.