Starting problems- 02 Triumph Thunderbird?

All of the oil and fuel settle out of the engine after sitting so it won't run the same until it gets the flow going again. The rings and pistons get coated creating better freer movement the same as anything made from metal. Depending on where you live the colder it gets the harder it will be to start. The battery has only so much life on it also, so if you have been charging it for a couple of years it may need a new one, they don't last forever even though you can recharge them. Good luck.