A CD player and its battery together do 500 kJ of work, and the battery also releases 250 kJ of energy as heat and the CD player releases 50 kJ as heat due to friction from spinning. What is the change in internal energy of the system, with the system regarded as the CD player alone? Assume that the battery does 500 kJ of work on the CD player, which then does the same amount of work on the surroundings.