RAID

From HighScalability blog:

"Crazy lessons from GoDaddy:  there is an inherent drawback to using a battery-backed write cache: Many RAID controllers, like our Dell PERC cards, go through a battery learning cycle which calibrates the capacity of the battery to ensure it does not unexpectedly fail. For us, this cycle occurs every 90 days. When a battery learning cycle begins, it fully charges, discharges, and then charges again, realigning the true capacity of the battery. While it performs the learning process, you cannot rely on it to sustain the cache in the event of a power failure."

...I need a backup battery for my battery, that backs up my RAID array, which creates a backup of my data.