battery - Prevent complete charging?

I'm looking for a way to prevent my phone from completely charging every time it is connected to my computer. I want to reduce the battery's capacity loss, as it is non-replaceable, and it seems to me that keeping the maximum charge at around 50% to 60% would be ideal. This chart, from this site, suggests that the benefit would be significant.

Capacity at    Discharge
full charge    cycles

100%           300 – 500
90%            600 – 1,000
70%            1,200 – 2,000
50%            2,400 – 4,000