This octet string lists the position numbers of any failed batteries on the array accelerator, with a zero-length string meaning no batteries have failed (or the controller cannot report individual battery positions). Since the accelerator's write cache relies on battery backup to survive a power loss, a non-empty value here is a direct signal that cached writes are at risk and the cache should be treated as non-persistent until batteries are replaced. For example, a returned octet of 0x02 tells the admin battery position 2 needs replacement before trusting write-back caching again.