Yes, the TSX Momentum PLC does have the capability of battery backed RAM by utilizing an option adapter.
This option adapter would be assembled between the IO base and the M1 or M1E processor.
There are three models available with part numbers as follows:
172JNN21032, one user selectable RS-232/RS-485 modbus port
172PNN21022, one modbus plus port
172PNN26022, two redundant modbus plus ports