I noticed that you were a 5*** team, so, Welcome to the CD! Over here, you will be able to find tips on everything you are wondering!
Here is a good thread on getting started
OK. Now, back on topic!
So if I am not misunderstanding you, your team is wondering where to mount the battery. There is no specific place to mount the battery. However, make sure that is is easily accessible and doesn't come in the way. Last year (2013), we built a battery cradle, fastened to the side of the robot. This was outside the robot, so the battery was very accessible. The cradle was lined with some foam weather seal, to secure the battery. And just to make sure no one was scared, we put a strap of velcro to hold the battery in place.
Try to keep the battery leads short. You may find it helpful to place the breaker near the battery. That will help with the engineering of the electrical system.
Keep the battery very low. Since it is so heavy, it will allow you to lower your CoG (Center of Gravity)
How large is your team? If it is large enough, you really need to create an electrical team. Our (Team 1165's) electrical team is two people because we don't have much for them to do!
"MAKE SURE THE BATTERY DOESN'T FALL OUT", as Magnets says!
Try to keep your design as simple as possible.
Make a DemoBot before the season starts, if you have the components and time. That way, you will know how to connect things together in your actual robot.
That was a long post. Anyways, good luck and enjoy the "sport of the mind!"