The D2 Forums

Yes exactly that.

Thanks MJ. I have trouble remembering things I did last week, let alone 8 years ago!
As delivered the battery had a red plug in a vent hole that instruction said to remove immediately, which I did.
This was however at the opposite end to where the vent pipe connects to my dying Yuasa, so I swapped the black plug from the hole at the opposite end assuming internally it's just one connected void.

Yes, its one common breather port. You just put the plug in the end you're not using