Hello,   The controller should go offline within a few seconds of confirming the operation. When it does, you'll likely see some messages about virtual disks not being on a preferred path. I would ignore those until the controller is online again.
I have an MD3620fc showing battery status Not Available and I think I should replace it. I have a replacement spare battery, but I'm not quite shure if just setting the controller offline will do the failover correctly of all Virtual Disks to the alternate controller, or if it must be done the change ownership manually. Anyway, is there any risk of I/O dusruption? Is it safe? All Virtual Disks is showing Write cache: Enabled (currently suspended). Battery status: Not AvailableLocation: RAID Controller Module 0Age: 1,713 daysDays until replacement: Not AvailableLast learn cycle: February 28, 2020Next learn cycle: April 24, 2020Weeks between learn cycles: 8Part number: PN D668JSerial number: SN 7578047S0356Vendor: VN DELLDate of manufacture: July 1, 2014 Battery status: OptimalLocation: RAID Controller Module 1Age: 1,713 daysDays until replacement: Not applicableLast learn cycle: February 28, 2020Next learn cycle: April 24, 2020Weeks between learn cycles: 8Part number: PN D668JSerial number: SN 7578047S0265Vendor: VN DELLDate of manufacture: July 1, 2014     I'd be glad for any help. Thanks Márcio
MD3620fc replacing controller battery