Tail Light Switch problems of the 2007 BMW 335

On 20 Feb 2013, we were driving on a highway in san francisco. Traffic in front of us slowed to a stop and we also stopped. We were then struck hard from behind by another car that hit the right-rear part of our bumper. Immediately after the impact, all interior and exterior lights in our car flickered and became very dim. We discovered later that the impact had damaged the car¿s battery, evidenced by electrolyte leaking out of the underneath, rear of the car. After the collision, traffic began moving again and the other driver moved his car off the roadway, leaving us sitting in the middle of a busy, 5-lane freeway after dark with no lights of any kind in or on our car. The emergency flasher flickered dimly, but was not working. All the head and tail lights were dark. Police eventually arrived and pushed our car to the shoulder. I waited inside our car while the driver spoke with the police. As I waited, the door locks suddenly latched and the alarm started. It was impossible to unlock the car from the inside. The door handles were completely non-functional. The windows would not open. I was trapped inside the car. People outside the car were unable to help me escape. A tow-truck driver asked me to release the hood latch. He attached a battery pack to some terminals in the engine compartment and when the interior lights came on, I was able to unlock the door and leave the car. Then he disconnected the battery pack and the car went dark. If there had been a fire or an injury, this would have been a very serious situation. As an engineer I see two, no-cost solutions to this problem. (1) surround the battery with a strong barrier and move it farther away from the rear of the car. (2) include a mechanical link to the door latches so that the doors can be opened from the interior of the car when the battery is disconnected.