How do I keep a MacBook battery charged to only 70%?

A chemist told me that a battery should be charged to and used between 30-70%, and its very bad for battery life to completely load or unload it.

He uses a utility program that always keeps the charge of his Lenovo laptop between 30% and 70%.

How can I achieve the same effect using Mac OS X?

Update (7 Years later): Its finally here, Apple introduces 'introduces battery health management': https://support.apple.com/en-gb/HT211094

This is now supported through a tool that edits charge level in SMC:

https://github.com/davidwernhart/AlDente

I have it installed on my Macbook 12 (2016 model) it's sitting at 70% plugged in.

I have used a piece of receipt from shop. It is thin enough to fit. The goal is to close middle connector. It is possible to close also 2 connectors at the left or at the right. For example close 3rd, 4th and 5th connectors, but leave free 1st and 2nd or conversely.

Based on this article:

• Use partial-discharge cycles
• Avoid charging to 100% capacity: why don't you unplug the charger now and then? Or try that software : http://fruitjuiceapp.com/ (Note: I haven't tried it myself...)
• Limit the battery temperature: make sure your laptop is well vented, and do not forget your laptop in your car during the summer.
• Do not charge your battery in a cold environment (<0deg Celcius). The charger circuitry is supposed to monitor the temperature but just in case...