No, you do not need to backup any registers before entering shutdown mode in the MAX17055. In shutdown mode, the internal LDO regulator is disabled, all activity stops, A/D register and fuel-gauge output values are lost but the MAX17055 still retains other important register values including battery parameters, configuration, and status. It is however recommended to save the learned parameters to nonvolatile memory periodically in case there is a sudden loss of power to the IC (not due to shutdown mode).