Hi TBone99
The "Deassert" state on the Disk Drive Bay 3 ROMB Battery 0: Failed means that battery for this particular sensor has not failed since the last power cycle.
The "Assert" state on the Disk Drive Bay 3 ROMB Battery 0: Low means that the battery for this particular sensor has reaches a low state.
In lay-mans term - your battery on Disk Controller is dim to failed and need to check or replace by you vendor.
Deassert/Assert are terms use in hardware sensors.