Forget what the charger says Dawn, charge it fully, and if you don't have anything other than a smart charger, then connect it in parallel with the battery from the ZT using your jump leads and leave it on charge for at least 24 hours.
I would be surprised if it's knackered if it's only three years old, even if it's been discharged to the point where the surface voltage across the plates is less than 7v (where a smart charger would see this as a fully charged 6v battery
) the trick of connecting in parallel with a battery not in such a deeply discharged state will bring it back from the brink.
Brian
