Backup battery

Backup battery is the name given to a secondary power supply, usually a direct current battery, to provide power in the absence of the main power supply.

An electronic device which utilizes a backup battery will normally get its power directly from a sustainable alternating current (AC) source or solar cells (DC). The backup battery will power the circuit only in the event of failure. The battery is otherwise charging from that same primary circuit.

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Examples

Computers

In computing, the use of a backup battery is quite common. This version is called a UPS or uninterruptable power supply in case of blackouts.

Another type is the real-time clock (RTC) or CMOS battery which keeps the computer's clock running even when the computer is switched off. It also serves to maintain the system configuration settings in Nonvolatile BIOS memory.

Burglar Alarms

Backup batteries are almost always used in burglar alarms. The backup battery prevents the burglar from disabling the alarm, should they cut off the mains power.

Performance Race Car Industry

Drag Race Cars at the starting line use far more electricity than their alternators can provide without tearing away precious horsepower. Recently the elite in the industry have switched to 16 volt batteries to compensate for this battery backup need. http://www.rockracingbattery.com/16v.php

Aircraft Avionics

Can you imagine being at 30,000 feet and having the engines go out? How about having the engines go out and then no electricity to run the controls? The FAA thinks this is a bad idea too! Therefore all commercial and private aircraft are required to have a deep cycle aircraft battery for their particular model. These documents are called "Type Certifications" or "Supplemental Type Certifications". Each owner must acquire one to change their battery. http://www.concordebattery.com/faapma.php