What's the best way to use the batteries?

[pop]

How low is it recommended to drain your batteries during flight? (for keeping maintaining long battery life). I have heard a wide range of things from stopping at 40-50%, 20-25% and 10-15%.
Obviously these are expensive batteries so I would like to use them in a way that would prolong their life and maintain them as healthy as possible. I'm more than willing to sacrifice some flight time if that means keeping batteries healthier longer.

 

[PdxSteve]

I bring it back with about 25% left and usually land with 10-15%. I bring it back at 25% in case there are last minute issues that happen from time to time so I like a little room to spare. Others seem to suggest landing AT 25%. It might be better for the batteries but I'd rather have 5min more flight time and buy a new battery in a few months.

 

[Marich]

I begin landing prep when batteries hit 35 percent, and try to be on the ground by 20. Just try to keep from dipping below 15%.

 

[Maddog]

You might find this useful:
80% Rule - TJinTech

 

[pop]

Is there any way to test if a Lipo battery has suffered any damages from over draining?