Do you want 500 charges or 1500 charges from your battery?

The Chevy Volt keeps the charge mostly in the 30-80% range as I recall and has the 8 year/100000 mile warranty. Effectively it only uses a maximum of 65% of its battery Maybe that is what you were referring to, or does Tesla do the same?

Unless you have a large expensive battery, most people are just going to charge to 100%. What we all can do is not to do a deep discharge and run the battery dry. If it has less than 50% charge on it, go ahead and fill it up.

Maybe a picture will help impress on you the importance of this?