Batteries have a positive and negative end that need connecting to an electrical circuit. In cylindrical batteries, the positive end consists of a small projection whilst the negative end has a flat base. Both ends of the battery need to mate with contacts, which are metal strips or springs that are found in battery holders or compartments. The battery contacts are connected by wire leads to the electrical circuitry within the device, so that when the terminals press against them, an electrical connection is made.
The most common types of terminal found in battery holders are coiled springs or spring contacts and flat tab contacts. Sometimes a battery is wired directly to a device rather than inserted into a holder. For these applications battery contacts are available which are designed for soldering directly onto the PCB. Once the contact is soldered onto the PCB the battery is then connected directly on to it.