I have two Mac book Pros:
- A 2013 Unibody retina that I use every day
- An older 2006 model with removable battery that I use a couple of times a month (when not in use, it's not connected to the AC. I recently replaced the battery, as the old one swelled apart).
I use them as desktop replacements, so I don't use the battery that often.
What's the best way to prolong battery lifespan? - If keeping the machines hooked up to the AC is a bad idea, then for how many hours each day should I use the battery?
Here is my research: There's a lot of conflicting advice.
A lot of sources, say you should calibrate the battery by letting it run down to 0% each month. For example, this Ask Different question, this Gigaohm article. All these articles were written in 2013/12 and cite Apple.com as the source for this advice.
However, the Apple.com page makes no reference to calibration. Is this because calibration is a bad idea, or is it because Apple no longer sells devices with removable batteries and so the advice is different?
Other sources, such as this AskDifferent question, imply that letting the battery drain is a bad idea, so using the AC whenever possible is actually a good thing.
Please note I am talking about the overall battery life span (e.g. the time the battery has before it needs to be replaced) and not increasing the day-to-day hours of the battery.