Doddsie, I have done exactly the same as you over the winter period since the early 70's. ie. starting the engine up and letting it run for a while and keeping the battery well charged. When I bought the Fazer a few years ago and told the dealer that I wouldn't be using it in the winter and it would be standing for around 6 months, he advised me to add fuel stabiliser. He told me that due to the ethanol content in modern fuels, if left standing for many months the fuel may 'go off', a condition known as stale fuel. Petrol containing ethanol is especially subject to absorbing atmospheric moisture, then forming gums,solids, or two phases ( a hydrocarbon phase floating on top of a water-alcohol phase).
The prescence of these degradation products in fuel tank, lines, carbs, or fuel injection components makes it harder to start the engine, or causes reduced engine performance. On resumption of regular engine use, the buildup is often eventually cleaned cleaned out by the flow of fresh petrol. The addition of a fuel stabiliser to petrol can extend the life of fuel.
After learning all this I didn't want to risk it so I took the advice and for the sake of a few quid bought fuel stabiliser. Yamalube is what I bought, available from many dealers.
If I hadn't bought the Fazer I would have carried on as I always have done as I knew nothing about fuel going off. Anyway, you know as much as I do now. Breakfast next, then off for a spin on the XJ600 which has never seen fuel stabiliser ! Have a good day and ride safely everybody.