For one to stop backfeed just simply add another diode.
Two, why waste time taking the backup battery out and putting new ones in, and buying extra ones, when you can just put this little circuit together and it will keep it charged enough to do what is was ment to do. Which is provide power for a short amount of time like when a motor sraws to much current or something.
If you think about it the normal use of the servos and camera which draw there power off of i wouldn't really be coming from the battery anymore as much as it would the little charger.
The backup battery is a major part since the servo's and the camera depend on it. It also help the OI and radio modem, out in case there was a real small cutout in the power.
So in fact its not just for the purpose of not wanting to take it out and charge it. It's also for the fact that there will be times that it won't be fully charged and having the little charger on the robot will help in those situations.
Besdies, its a good learning experience for the students, isn't that what FIRST is about?
