Question on battery box venting

[suburbancowboy]

This weekend I built my battery box.  It is approximately 18"X18"X7'.  It will hold 8 6Volt golf cart batteries(New system) and 3 12 volt deep cycle batteries(Old system).  Don't worry I wont be mixing the two.  Old system will be shed power only.  Any way the battery box will be sealed and I have been thinking about how to vent it. 

My preference would be a passive system with a hole at the bottom on one end, pipe to outside, and another hole at the top vented to the outside on the other end.  This will be under the over hang on the shed so snow will not be an issue. 

Question
1. For the passive solution what size of holes would be sufficient?  1" or 2"
2. Or with this many batteries enclosed do I really need a power vented solution on some kind of controller. 

Every thing on the net I see that says I need a power vented solution is coming from vendors.

[Squirl]

http://www.homepower.com/articles/solar-electricity/design-installation/battery-box-design

The inside of the box should be carefully caulked, and painted or treated with a penetrating sealer to resist minor spills or corrosive vapors. For best results, a liner of 40-mil EPDM rubber or pond liner (available at many nurseries or home improvement stores) is placed in the bottom and about 6-8 inches up the sides, folding instead of cutting for the corners. This liner protects the wood and forms a leakproof container to contain any accidental spills or leakage from the cases. Above this level, typically three 1- or 1 1/4-inch inlet ventilation holes are drilled across the front.

The vent is typically made of 2-inch PVC water pipe or the equivalent. Larger sizes of PVC pipe may be used, but excessive venting can let too much heat escape in winter. The exhaust vent should exit through the building wall or roof, with all laterals rising. An insect screen should cover the outside end, with protection from rain and snow entry.

Unless you put a lot of bends in your vent, I wouldn't worry about power venting.  I've personally never seen or heard of them in smaller residential systems.  Hydrogen is the lightest most expansive element in the known universe.  It doesn't want to stick around.