computer battries

        Modern personal computer motherboards have a backup battery to run the clock circuit and retain configuration memory while the system is turned off. This is often called the CMOS battery. The original IBM AT, for example, used a small primary lithium battery to retain the clock and configuration memory. Modern systems use either primary or rechargeable batteries. Primary batteries required periodic replacement; rechargeable types often lasted as long as the system they supported.

Backup batteries are used in uninterruptible power supplies, and provide power to the computers they supply for a variable period after a power failure, usually long enough to at least allow the computer to be shut down gracefully. These batteries are often large sealed lead-acid batteries.

Server-grade disk array controllers often contain onboard disk buffer, and provide an option for a "backup battery unit" (BBU) to maintain the contents of this cache after power loss. If this battery is present, disk writes can be considered completed when they reach the cache, thus speeding up I/O throughput by not waiting for the hard drive. This operation mode is called "write-back caching".

aircraft emergency battries and burglar alarms

                 Backup batteries in aircraft keep essential instruments and devices running in the event of an engine power failure. Each aircraft has enough power in the backup batteries to facilitate a safe landing. The batteries keeping navigation, ELUs (emergency lighting units), emergency pressure or oxygen systems running at altitude, and radio equipment operational. Larger aircraft have control surfaces that run on these backups as well. Aircraft batteries are either nickel-cadmium or valve-regulated lead acid type. The battery keeps all necessary items running for between 30 minutes and 3 hours. Large aircraft may have a ram air turbine to provide additional power during engine failures.

Burglar alarms

      Backup batteries are almost always used in burglar alarms. The backup battery prevents the burglar from disabling the alarm by turning off power to the building. Additionally these batteries power the remote cellular phone systems that thwart phone line snipping as well.

battry backup

      A backup battery provides power to a system when the primary source of power is unavailable. Backup batteries range from small single cells to retain clock time and date in computers, up to large battery room facilities that power uninterruptible power supply systems for large data centers. Small backup batteries may be primary cells; rechargeable backup batteries are kept charged by the prime power supply.

     A battery room is a room in a facility used to house batteries for backup or uninterruptible power systems. Battery rooms are found in telecommunication central offices, and to provide standby power to computing equipment in datacenters. Batteries provide direct current (DC) electricity, which may be used directly by some types of equipment, or which may be converted to AC byuninterruptible power supply (UPS) equipment. The batteries may provide power for minutes, hours or days depending on the electrical system design, although most commonly the batteries power the UPS during brief electric utility outages lasting only seconds.

Battery rooms were used to segregate the fumes and corrosive chemicals of wet cell batteries from the operating equipment; a separate room also allowed better control of temperature and ventilation for the batteries. In 1890 the Western Union central telegraph office in New York City had 20,000 wet cells, mostly primary zinc-copper type, in use.