All the ones I had flew for several minutes on a 15 minute charge. There is no new battery for the heli. These do not have any user-serviceable parts. It is put in by the factory and you throw it away when it stops working. But the failures were always with the mechanics or with the electronics. The batteries kept going after a hundred charges (on the few that worked well enough to keep using)

Channels refer to the control features supported between the transmitter and receiver. Not individual frequencies for each channel, but rather coded data sent on the one frequency the Transmitter uses. Two channel helis have the main throttle on one channel, so that the heli can go up and down, and the rudder, or yaw control, on the second channel so that you ca turn the heli. There is no provision for forward flight. You typically add a bit of weight to the nose so that the heli always drifts forward slowly the entire time it is in flight. A three channel heli adds elevator, or pitch, control. You can make the heli lean forward and back, so you can control forward and rearward flight. A four channel heli adds roll control, so you can fly left and right (like a crab).
The next step is typically a six channel heli, adding gyro control and collective pitch. These are the helis that can do ore aggressive stunts, like inverted flight.

Before you buy, read and ask question on the dedicated RC heli forums. You will learn a lot, and get better information.

Good luck!