A dialysis monitor with a treatment fluid path configured to provide treatment fluid to a dialyzer when dialysis treatment is performed by the dialysis monitor is provided. A battery unit is connected to a controller and at least a portion of the functional elements of the dialysis monitor in order to provide back-up power should the supply of external power be discontinued. Energy of the battery unit is used to provide energy to the heater in preparation for and/or at least partly during thermal disinfection of the treatment fluid path or when starting up the preparation of treatment fluid thereby shortening the time required for the thermal disinfection and the starting up of the preparation of treatment fluid, respectively.
