Battery duration, charging and balancing

I've four batteries: 3 x 2600mAh 3S 20C, and 1 x 3300mAh 3S 20C. They last between 7 and 8 minutes, depending on the flying mode, camera on board.

With the charger you can balance the batteries or charge them. Some people charge them and only use the balance option every 5 or so flights, when the difference between the cells is high. I've been doing this for long time, until someone told me the best is to balance them always. There's a lot of discussion as well about this matter, so at the end I guess you do what it works for you! :)

To fully charge/balance the batteries requires about 45 minutes, depending how much you drain the battery :p. I've a voltage alarm that beeps at 3.70 per cell to stop flying and avoid damaging the battery.