Batteries can last for 10 years or a year. Batteries that are used last better than those rarely used.
Take your battery off and connect it to your optimate or whatever you trickle charger unit you have.
May desulphate and come back to life but may end up weak.
Cold weather normally sorts batteries out and many will fail when the temperature drops.
If you are not using a bike for a long time especially over winter, remove the battery from the bike, charge it up and store it inside and top up charge every 4-6 weeks. Otherwise use a battery tender on the bike.
For what they cost and for the inconvenience of a knackered battery, if in doubt get a new one!