This a battery (lifting) jack to be used in a tub with adjustable backrest that provides the patient with a high degree of independence. Its large sitting area with wide side parts provides a large sitting area for a safe move. It is easy to control by using a simple manual operating device serving for lowering and raising both the (lifting) jack and the backrest. Ergonomic shape of the operating device can be operated with one hand. The operating device is light, waterproof and swims in the water. The (lifting) jack is coated with a soft antiskid material that can be washed in a washing machine. The (lifting) jack was tested and it meets all safety requirements.