1999 C230 has a recurrent issue with the windows, sideview mirrows not working, and sometimes the trunk will not unlock. I have replaced the battery as I have noticed that the battery voltage stayed around 12.4vdc. I have recharged the battery to 12.8 vdc and the windows will work and stay working as long as the battery voltage is in that range. The Car will crank up and runs fine at either voltage readings. The replacement battery also gave similar readings after a few weeks and all symptoms return. Charge voltage while the car is running is ~13.8 vdc but the battery will return to the lower voltage after a while. The battery will not discharge completely when stored for several weeks so I dont perceive a voltage short anywhere, just that I have to keep resetting the system via disconnecting and reconnecting the ground terminal. An OBDII scanner I have returns no fault codes. Any ideas guys?