Which battery to use

[Nomad54]

I am restoring a bsa a10 alternator model which I will be using the alternator to supply the electrics. There will be basic head lights, tail lights, stop lights, horn and May fit indicators later so what I need to know is what size 12volt battery I need to fit.
Tom

[berger]

i would say the biggest amp hour one that will fit in the space.