I would agree with Ollie above, especially in that all brands seem equally rubbish nowadays and it’s the luck of the draw if you get a good conventional lead-acid one that lasts.
If you are going with a smaller 12v YB5, you could cut down on power usage by fitting a 12v Ultra-bright LED parking light bulb in the headlamp (BA9S) which is brighter than using a dipped headlight with a conventional bulb if you are using the headlight as a day riding light. (Available on eBay)
If you are feeling flush you could fit a Lithium battery – I put a JMT YB5 on my Supa5 with Vape Powerdynamo and it worked fine.
It is the same size (120wide x60deep x92high) as the 6v original so fits in the space, only weighs 420grams and they tend to maintain their charge if not being used, like over winter perhaps, in fact they don’t recommend trickle charging them.
If you do need to charge it however, you should use a specific charger so factor that in!!