Is it possible to use an 18650 battery to charge a cr2 battery rated at 3.0v? If so, what voltage should the 18650 be before connecting it to the cr2 battery? cr2 battery is this one: http://dx.com/p/rechargeable-3v-cr2-800mah-green-2-packs-932 rated at 3.6v to 2.0v.
That is a very bad idea, just buy a suitable charger and do it the safe way.