I don't believe that a heli that comes stock with a 1200mah battery will have either the space or lifting capacity to use a 3000mah battery. Check the dimensions and weight of the battery you're currently using and do the same for the battery you're looking to buy, make sure the new one will fit in the battery compartment. If the battery goes at the front of the heli then increasing the weight will make it nose heavy.

You're current charger would work but for a 3000mah battery would take 3 times as long to charge.

I suggest you look at something like a 1500 to 1800mah battery which would be more reasonable.