*There is no magic BMW battery. Does it fit in place, can it get buttoned down, does it have enough CCA, can you connect it, and will the vent work? Sofa King Good! I used to hotrod, and I'd put the battery in a vented box in the trunk or on the floor, and there's no mystery science involved. You CAN get "ventless" glass pack batteries- bikers and hotrodders like to get them because you can mount them on their side, or even upside down, if that's the best way to access the terminals.
*I still believe the guy got took. IF you plug up the vent the battery could explode. IF you don't vent the battery to the outside you could experience vapors and fumes in the trunk. IF you apply some common sense these things won't occur.