Wowee, what's that smell? Oh yeah, it's the smell of a thread that's been dead for six months getting dug up!
Seriously though, if you still have no joy with a fresh battery and the bikes been stood for years then pull the carb off & give it a clean out. Unleaded petrol has a nasty habit of rendering itself unusable after about 7/8months standing, gumming up anything it touches in the process so most likely you'll find that the jets are blocked with gum & the float needle sticking.
Needless to say, you need to drain the tank & use fresh fuel no matter how much is left in it. It would also be good practice to strip and clean the tap & rinse out the tank with fresh petrol too.
Just one more thing, when you clean out the carb jets don't -DO NOT- use wire/paperclip or anything like that as it will damage the precision drilled hole making the jet useless. Compressed air is the usual way to go, but I find that MZ's advice of using "a bristle from mother's brush" (it really says that in my TS250 handbook!) can be invaluable for clearing more stubborn gunk, along with an overnight soak in carb cleaning fluid. And remember, where fuel systems are concerned, cleanliness is waaaaay ahead of godliness.
Best of luck, any other problems just start a thread for them.