Plug in the battery all the time

John Galt--

Based on Apple's new Battery Health Management feature, I think your advice (that one needs to unplug and run on battery periodically) is not quite up-to-date for MacBook Pro 2016 and later running Catalina 10.15.5.

Catalina software 10.15.5 for MacBook Pro with T2 chip (2016 models and later) includes a new feature called Battery Health Management. Based on your usage patterns, this widens the hysteresis to initiate a charge cycle at a lower level, and stop before 99 percent.

About battery health management in Mac notebooks - Apple Support

https://support.apple.com/en-us/HT211094

This relaxes the set points around re-charging (based on your usage patterns) and can improve long term battery lifetimes. When active, recharging may stop short of 100 percent charged.

#1 is not correct. Your Mac is always free to "borrow" additional needed power from the battery. But it only does that under the heaviest of loads, and that is part of what produces its excellent performance under heavy loads. It never switches to all battery power when a Power source is connected.

#2 is exactly right. By widening the low limit (and possibly the high limit as well) of when a charge cycle is initiated, it produces fewer charge cycles.

The down side is that if you suddenly need to take your MacBook Pro into the field for extended operation on battery, there is a slight chance it will be at less-than-maximum battery charge when you disconnect it from power.

We could read from Apple's description of the feature that this is based on your individual pattern of use. The less often you run it on battery power, the more likely it will be at less than peak charge when you press it into battery-operated service.

No.

Leaving a portable Mac's power adapter connected all the time will reduce, not extend, its service life.

To learn how to maximize your MBP's battery life and lifespan read About Mac notebook batteries - Apple Support.

Leaving the computer plugged in will not damage the computer or battery. I leave mine plugged in when convenient to do so. Leaving the computer plugged in will reduce the rate of accumulation of battery cycles.

Could you please explain what is "service life"?

It describes the period of time for which the battery can be expected to perform well enough for you can use your Mac without having to plug it in. You should expect it to last for years, perhaps as long as you want to keep using that Mac before deciding to replace it with a newer one.

So leaving the macbook plugged in when possible VS not plugged in, which one is better?

Neither one is better, but if you want your MBP battery life to last a long time it needs to be exercised regularly. Plug it in when it's convenient to do so. If you leave it plugged in literally all the time as you asked, it won't last as long as it would if you were to use it once in a while.

You don't have to obsess about it. It's been my experience that the less you pay attention to a Mac's battery (or an iPhone's, for that matter) the longer it will last. That anecdotal observation is not intended to represent anything close to a scientific method.

Grant Bennet-Alder wrote:

John Galt--

Catalina software 10.15.5 for MacBook Pro with T2 chip (2016 models and later) ...

All very nice to know.