Servos can usually be plugged right into your RC receiver and draw power directly from your battery. However, you should check to make sure your servo can handle the voltage supplied by your battery.
Batteries are usually rated for their capacity (e.g. mAh), not current, so you might want to double check your battery rating. You might find this blog post on battery capacity helpful. If your battery cannot supply enough power for all the things in your application, you probably need a more powerful battery.