Ive just bought a 110amp battery from Halfords. Fitted it in the car-park, alongside (in line) the existing battery.
So, its a 5 minute drive back from Halfords to my place and Id say the temp was markedly improved on the circulating water by the time I got back here. I suspect the original battery therefore isn't holding its charge, so probs time to change that one and have two brand new 110 amp units.