How to recharge Macbook’s battery

There are any number of opinions on what can be done to maximize the life of a lithium rechargeable battery. But for the most part I would say that it's easier to just not worry about it. Use the battery however you feel is convenient. If you use it connected to the power adapter nearly all the time, I think it's a good thing to at least use it on battery power occasionally. If the battery loses capacity, you can eventually have the battery replaced.

The only thing I would caution anyone regarding a lithium rechargeable battery is that if you ever let it go into auto shutdown where it saves the state to the drive, make sure that it's charged again quickly. The one thing that can severely reduce battery life (or even kill the battery) is getting it into a deep discharge state. "0%" isn't really the absolute floor. There's a certain amount of a safety margin built in to 0% such that it shouldn't get to a deep discharge state unless the user fails to charge it. The battery will self-discharge, and eventually it will get to a state where there will be permanent damage.

If you want to learn more about battery longevity in general, the site batteryuniversity.com is pretty good.

I know I said it's not worth worrying about, but if you're really all that concerned about getting the battery (when actually used on battery most of the time) to last the absolute longest time, then maybe the whole 20-80% regimen would be ideal. Some computer power management systems can do that automatically when programmed by the user. The center of the charge range is often called the "sweet spot" because keeping the battery in this range is likely to cause the least amount of degradation. However, Apple doesn't have any automatic way to set it to do that.

If you really want the battery to last the longest, using it connected to power most of the time will reduce the number of charge discharge cycles. That's generally how I've used my Apple notebook computers over the years, and I've never replaced a battery. I have however had a severely degraded battery where I stopped using it and it discharged in storage.

This is a complex question, and you have hit upon two factors that work against each other. Keeping the battery between 20% and 80% is good if you use the computer on battery a lot. But as you point out, keeping it charged to 100% reduces the number of full charge cycles, which keeping it to the 20-80 range does not; that actually significantly increases the number of full charge cycles. There is a crossover point somewhere, but knowing where it is would require years of research and is probably different for every user. I know electric cars generally use the 20-80% rule, but they are constantly being discharged and charged; they are never kept at 100% for long periods of time.

So your original answer is the best; do what is convenient.

My MBP battery started to swell at the 4 year mark (it is plugged in most of the time). Apple replaced the whole computer for the cost of the battery ($150). So $150 for 4 years of use on a $2200 computer was a good investment.

Read Lawrence's User Tip that I linked to above. He's kind of the resident expert. The 20-80% won't make any difference. However, you're correct in that you should make sure the battery is at least have charged before storing for any length of tiime.

You might want to take a look at this article:

When to charge your iPhone or iPad - Apple Community

I heard the “sweet spot” description in reference to hybrid car batteries. Those batteries really only need to provide short term, supplemental output so using the entire battery range isn’t critical. Also, losing capacity isn’t that important since a small range is adequate.

I’ve has weird luck with batteries. Ever seen a Mac battery reporting negative capacity? Mine went between that and reporting good health. Until it started swelling. But that was a polycarbonate MacBook with a replaceable battery. It swelled out rather than in.

Use your MacBook with the power adapter when power is available. It will not overcharge.

When power is not available, use it on battery.

Do not anguish over it.