The windows will need your key to be in position 1 at least. The radio will work without the key. Just press on the volume knob, or press on the "Audio" button on the top-left of the receiver.

I have not timed this, but if the car has not been fired up, the radio will shut itself off in about 30 minutes. You can again press the volume knob or audio button and restart it.

I have run the radio for around 90 minutes once. Perhaps I was on the brink of battery drainage? How is a man supposed to wax in silence?

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2008 ML320 CDI | Iridium Silver | Black ARTICO Leather | Premium Package (H/K Logic7, Parktronic, Rear Heated Seats, Rear Power Hatch, DVD Nav, 10-way Front Seats w/ Memory) | Backup Camera | Aluminum Running Boards | 4500K MTEC Low-beam HID | 30% Metallic Tint | Boomerang2 Recovery System | Weathertech Front Floorliners | Bridgestone Blizzak DM-V1 Winter Tires