Lenovo ThinkSystem DE Series Hardware Installation And Maintenance Manual page 101

If this green LED is on, the controller is still using battery power. You must wait for this LED to go off
before removing any components.
Internal Cache Active LED
Step 3. Locate the blue release latch for the battery.
Step 4. Unlatch the battery by pushing the release latch down and away from the controller canister.
Battery release latch
Step 5. Lift up on the battery, and slide it out of the controller canister.
Step 6. Follow the appropriate procedures for your location to recycle or dispose of the failed battery.
Battery
Battery
.
Chapter 3 Hardware replacement procedures
95