While you lift and lower the battery during the procedure, grasp the blue handle on each end  of the battery and keep the battery parallel to the canister system board, as shown in  Figure 12-15. Important:  During the replacement, the battery must be kept parallel to the canister  system board while the battery is removed or replaced. Keep equal force, or pressure, on  each end. For more information about the BBU replacement process, see IBM Knowledge Center. For more information about replacement procedures, see this website. Two expansion canister slots are on the top of the unit. As with the control enclosure, the left  slot is canister 1 and the right slot is canister 2. Figure 12-16 shows the rear view of a fully equipped expansion enclosure. SAS ports are used to connect the expansion canister to the node canister or to an extra  expansion canister in the chain. Figure 12-17 shows the SAS ports that are on the expansion  canister. 634  Implementing the IBM Storwize V5000 Gen2 with IBM Spectrum Virtualize V8.2.1 SAS ports 12.2.3 Expansion canisters Figure 12-15 BBU replacement Figure 12-16 Rear view of an expansion enclosure with two expansion canisters