According to official Dell PowerStore documentation, both the Battery Backup Unit (BBU) and the Nodes are classified as Customer Replaceable Units (CRUs). A CRU is a component designed to be replaced by the customer without the need for a certified Dell service technician. The PowerStore architecture's modular design facilitates the straightforward replacement of these components to simplify maintenance and maximize system uptime. The replacement procedures for both nodes and BBUs are fully documented for customer execution. Therefore, both options are correct.

A. Base enclosure: This is the main system chassis and is a Field Replaceable Unit (FRU), requiring replacement by certified Dell service personnel.

B. Expansion enclosure: This is also a major hardware chassis classified as an FRU, meaning its replacement is a service task performed by Dell.

1. Dell PowerStore: Hardware Information Guide for PowerStoreOS 3.0 and Later. In the section "Replaceable units," Table 1, "Customer-replaceable units (CRUs)," explicitly lists both "Battery backup unit" and "Node" as CRUs. The same document lists "Base enclosure" and "Expansion enclosure" as Field-replaceable units (FRUs) in Table 2.

2. Dell PowerStore: Service and Supportability, A Dell Technologies White Paper. Page 6, under the "Customer-replaceable units (CRUs)" section, states: "PowerStore appliances are designed with many customer-replaceable components... These components include drives, power supplies, I/O modules, fans, nodes, and battery backup units (BBUs)."

3. Dell PowerStore: Replacing a Node in a Base Enclosure, Dell PowerStore Service Procedures. This official guide provides step-by-step instructions intended for the customer to perform the replacement, confirming the node's CRU status.

4. Dell PowerStore: Replacing a Battery Backup Unit, Dell PowerStore Service Procedures. This document provides the official, customer-facing procedure for replacing a BBU, verifying its classification as a CRU.