According to the website, the SAS controller on the server SYS-1026T-6RF+ is integrated on board. The website always says that you can put in a battery back-up but does not specify which model to use. What is the model of battery backup for the SAS controller?
You can use the BBU part number BTR-0018L-0000-LSI for the 1026T-6RF+ SuperServer. Also need the battery kit (BTR-0018L-kit) for the bracket and extension cable to connect the battery and secure on chassis.