The write cache is memory on the RAID controller which could greatly increase your write performance. However, since the risk of data loss if there is a power failure the controller card wants a local battery which could hold the unwritten IOs until power returns.
You would have to check the specifications for this specific server and the version of the RAID controller to see which features it supports. When the server is rebooting you could enter the Controller "BIOS" and see which options you can change. There could also be vendor CDs, like HP Smartstart, which you could boot the server and perhaps get more visibility into the controller setup.