I too read the 50% capacity rule, but I read it in a very professional battery book, but I remember the gains were very minimal. Something like 10-15% increase in lifespan. When a battery is only lasting 2-3 years as it is, that is less than half of a year.

Going back to my link, it looks like 50% is the sweet spot in the DoD chart; multiplying the number of discharges by the DoD results in 50% DoD being the highest return on capacity.

But...also remember in an application where you can use the device while its charging changes the concept of maximizing life span. I don't believe the act of discharging will avoid shortened lifespan, but rather it avoids degradation on the battery CAUSED by discharging itself.

Batteries hurt my brain...