After a period of time (roughly 2 years) the performance of the BBU will begin to deteriorate, impacting the RAID performance. If the BBU is in a charging state for longer periods of time then the disk array will remain in Write Through mode for an equally longer period of time. During boot you can check the Raid BIOS Console to see if the battery has reverted to Write Through mode.
Symantec Security Information Manager does not ship with the files that will allow you to test these batteries from a command line without rebooting and breaking into the Raid BIOS. You can download the tool from this document.
One you have download the attached MegaCli_SIEM.tar below are the instructions for installation:
If the batteries are showing in a degraded state, please contact support to arrange replacement.