Install BDU in a temperature chamber, decrease the temperature in steps of 5oC from 20℃ to -35℃ and then increase the temperature in steps of 5℃ from -35℃ to 55℃. Wait at each step until the BDU has reached the new temperature.Supply 12V to positive and negative contactors.Supply 450V 225A (1C) to B+ and B- input. Using resistance to connect Dischage + and Discharge - as load.