Battery Charging Flight Power 6S 2500mAh 22.2 Volt

[Pipes]

I would like to know when I take my firts flight with my T-Rex 500 when should I put the heli down. Once I see the power is getting less. Do I time my flights, I am new so i will be doing regular flight. Is it important not to fully run down the battery. Then when I charge the battery do I need to balance it on every charge and when should I discahrge the battery and charge etc. I see so many diff ways people are doing this so I am getting confused. The battery is very expensive so I don't want to ruin it.
Also someone said not to go below 80% of the battery how do you know this when you are flying?
Thanks for any help

[poisike]

I time my flights, i can hover for 7 minutes and back goes 1900mah with Flightpower 6S 2500, 12t pinion and throttle curve (Idle up 1) 95% - 90% - 85% - 90% - 95%, but i set my timer 6:30 just to be on the safe side. I always balance charge my lipos.

Hope this helps. I'm new to this hobby also and my English is not so good, hope You can understand.