The GigaRAID/FT's Model 1300 Battery Backup Unit (BBU) is required for the storage-system cache and may be installed in a Model 1100 to upgrade to a Model 1300. In the event of a power outage, the BBU allows the Storage Processor (SP) to shut down the storage system in an orderly way. The BBU can provide up to 60 seconds of power, which is sufficient for the SP to empty its cache by writing data to the physical disk units. To conserve power, the SP shuts down all unnecessary disk drive modules while emptying the cache. Once cache data is safely stored on the physical disk units, the SP disables the BBU to preserve the life of its internal power cells. When power returns, the BBU recharges its cells automatically. The BBU may be installed or removed while the disk array storage system is running.