I have already done a page — or two on building the battery boxes but this entry is about testing an electric vehicle battery box to make sure there is air flow when charging and make sure no hydrogen is entering the passenger compartment.
In the SS Saturn there are 4 battery boxes. Two in the front under the hood where the radiator was. There are not sealed but vent into the under hood area and outside.

Building the 2 rear battery boxes

Battery Boxes and connecting pipe

Two battery boxes in the trunk area are the ones that venting and cooling are critical. Critical to ……
1. make sure hydrogen which is created only during charging is pulled out and not enter the cabin area
2. to keep the normal sulfur smell down
3. somewhat control the batteries temperature

The rear boxes were built with 3/16″X2″X2″ angle iron and lowered halfway under the original body sheet metal to improve handling. The 6 sides of each rectangle box is made with 1/2″ plywood. The lids are bolted down with reinforced steel and sealed with weatherstripping. The forward of the two boxes is directly behind the rear seat back. In fact the seat back is moved forward 6″ to accommodate the box.

Rear Battery Boxes Finished

Battery box vent inlet in winter mode

The rearward box of 8 batteries is about where the spare was. The two boxes are about 8″ apart (there is a frame between the two). The two boxes are connected with a 1.5″ diameter pipe that one of the 2/0 cables and a charging wire run inside. This pipe is also important because that is where the air flows when the batteries vent. The rear of the rear box has installed a ventilation fan that only runs when charging. The fan is 120VAC and is directly wired to the input side of the charger. This brushless electric vehicle battery box fan PULLS air not pushes. That is important. The rear box is sealed except for the opening to the fan at its rear and the opening to the connecting pipe at its front. The forward box is only opening besides the pipe at the rear is a 2″ hole under the vehicle. This opening gets some ram air effect while driving and allows cool air when charging and the fan pulls air form there. The opening can be partially blocked in the winter with duck tape or etc.

This video is about testing the battery boxes using smoke generated by a smoke machine that uses a special liquid which is mostly corn oil. In the video you can see the smoke following the air currents drawing into the inlet and out the outlet inside the rear bumper. You can check in the passenger compartment for any smoke and then repair the leaks.

This 144 Volt Diagram Shows the Final 3 Battery Packs and battery layout