So I opted for a Lithium battery. 0.9Kgs instead of 3.7Kgs and the bike starts better than it ever has. Streets cheaper than the standard battery too, well happy. At least I will be as long as it lasts 10 years.
Only downside is that if it goes flat I'll need a special charger that doesn't exceed 14.4 volts. My modern clever one would on desulphate mode and my ancient car charger (inherited from my FiL 31 years ago) runs up to 14.9 volts.
My new CCM has a LiPO battery and my Honda CT is still on its original battery from 2014 . For now I have bought an Optimate Duo charger for around £35 from a dealer which will specifically charge LiPO batteries and also standard lead acid / AGM.