There is really no need to run an extra battery in your glider. If the ESC has a BEC it will cut off power to the motor before it runs out of power for the radio. Actually it is kind of a hassle to have a separate battery to run the radio because you now have two batteries to charge. The guys running an extra battery are usually your hot liners who can draw a lot of amps and just about kill the battery. I was using a 2250 25c 3s battery in a 100" ws Nomad and got three launches to 400', using about 1700 ma from the battery, flight time of about 30 minutes plus. This Sunday I installed a 3700 25c 3s battery, after rebalancing the glider I came up 3 ounces heavier, I had to add 1/2 oz in the tail. Originally when using the 2250 battery I had to add 2 oz. of lead to the nose. I got 5 launches to 400',using about 2900 ma in a fifty minute flight. I am still experimenting with props. Hit a huge boomer which took the glider to over 800'. At 100" ws
the Nomad was getting a bit small soaring overhead, I had a dickens of time trying to get out of that thermal. Always be sure you have a solid connection between your battery and ESC, you don't want a flyaway. When soaring to higher attitude it is easy to lose sight of your glider.