Oil change + replace battery, which comes first ?

The age of the gas is a concern. The gas in our Mh is probably a year old too. I run it periodically and it seems fine but if it gets much older I don't know what to think. I have vintage cars that don't get much use but I haven't had an issue with the gas in them. I have had more trouble with small engines that do not hold much gas. Staybil or seafoam would possibly help.