Battery size/brand?

[MikkiJayne]

Yes exactly that.

[HPsauce]

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.

[MikkiJayne]

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