The 80-20 rule only counts for batteries that directly report their state of charge, because they don’t have any logic built in, for instance. Most laptop batteries will have a separate management system that’ll hide the top x% and the bottom y% to prevent over/undercharging, and probably apply some calibration to those numbers as well (because state of charge doesn’t necessarily deplete linearly). However, not going down to 0 and up to 100 does generally save the battery, despite the increased amount of charge cycles, as the most wear is done during deep drain and high charges. Temperature also strongly affects battery lifetime. In practice, very few people actually do the 20-80 thing, though. It’s just too much of a pain manually.

Many modern laptops also tend to have management systems that’ll allow you to pick a minimum/maximum state of charge and let you cycle between them while the cord is connected. I don’t know if Apple implements that, and if it works on Linux, but on windows there’s usually a tool for that. There are also laptops that’ll let you decide on a minimum and maximum percentage, so that the device can charge up to “100%” and drain to “0%” while actually doing 80-20.

I believe most MacBooks have battery management capabilites to set minimum and maximum values. You should check online for details about your laptop’s model and year, there’s probably a tool you can download to configure all that. For instance, there’s this Gnome extension that also had a handy guide for manually setting limits.

The most important part with batteries is to check if they start swelling up. You can have a (badly produced) brand new battery that swells up after one use, or one that’ll work for a decade, it all depends on how lucky you get. With a ten year old laptop, you’re probably already in “can become a lithium balloon” territory.

That highly depends on your model.

1. Yes normally once the battery is fully charged, it should run from the charger. Probably runs from the charger directly but also charges the battery.
2. The OS can limit the battery charging start and stop point. COSMIC desktop has such a feature. It may need interaction with the EC though.
3. Yes, if the laptop is just running off the AC, charge it to 50% and keep it there. If not, then cycling between 20/80 is best. But that is unlikely, my 2012 thinkpad also runs direclty off the charging brick.

You could try to uninstall the battery and just put an AC cable in. My laptop works like that.

One option is to leave it plugged in and hope the charge controller isn’t stupid. There might be a bios option for AC mode or similar, dunno how custom the firmware on these old macbooks is.

Try to cycle it once every two weeks or something. Unfortunately there isn’t much of a right answer to your question, there are advantages and disadvantages of both approaches. This is a good read on the subject: https://batterycare.net/en/guide.html

Just charge it and use it. Recharging and discharging the battery shortens the life of the battery. In an ideal world, you would charge the laptop battery to 50% and then never charge or use it again, but that’s makes your battery fucking useless.

So use your laptop. My advice is to keep it plugged in as much as possible. Most laptops (even 10 years ago) can run directly off the wall power, which stops the battery from degrading (as fast) as older laptops where they were constantly powered by the battery, and the charger just kept it topped off.

Most of the battery advice you hear is just voodoo bullshit, or it makes a very small difference in the overall life of the battery. Just use your computer like normal.

As long as it is still running you should be fine, but it’s better to keep your battery around 80%. There are tools that block the charge until you ask for a full charge when needed

When MacBooks are plugged in, they get their power from the charger. They are not simultaneously draining and charging the battery in general, unless they need more power than the charger can provide (unlikely unless you are using a charger with lower wattage than the official charger that came with your laptop).

I was not able to find an official source on this from a quick search, but if I remember correctly, this should be true for any moderately recent MacBook. Maybe any MacBook at all, since they only started making “MacBooks” in 2006 and then tech hasn’t changed much since then.

Personally, I leave my MBP plugged in during use whenever possible, and I typically unplug it at the end of the day. You don’t need to unplug it, but hey, it’s a good idea to unplug anything that doesn’t need to be plugged in, just to save power.

My son has a gaming laptop that is plugged in constantly. I vaguely remember reading that all modern laptops protect the battery to some degree, though not sure how. I’m guessing it is by using the mains while charging. Not sure what the damage is to a battery that is constantly fully charged.

Just keep the battery at 80%

It’s a miracle that the battery is still working at ten years. The most realistic thing is to just keep up with your backups, and be ready to dispose of that laptop the moment the battery starts swelling.

Yeah you don’t want the battery to sit at 100% or 0%. I just bulged out my 10 yr old work macbook battery by leaving it plugged in, not the first one i’ve seen either. There are utils that can set charge limits in linux https://askubuntu.com/questions/34452/how-can-i-limit-battery-charging-to-80-capacity

TBH you MBP battery is probably nearing EOL but it may actually be replaceable.

is a 10 year old macbook pro

10+ years old laptop batteries have a habit of dying eventually. And some of them (not many) cause a fire then - especially while charging up.

I have seen it - well, 3 hours later in the morning then.

I would not leave this device alone with the power cord plugged in. Charge it only while you are there, so you recognize it, if it decides to heat up someday. Then have a metal bucket ready to carry it outside.

No it’s got a charge controller that keeps it from fucking up the battery.

Source: I’ve owned many macbooks and worked on many more. The documentation and best practices for both implementing charge controllers for lithium ion batteries and the specific best practices for computers and phones with lithium ion batteries.

Your battery ought to be replaceable once the bottom panel is off the case. Just unplug it and use alcohol to weaken the glue while you scrape it out. New ones are less than $100.

E: if you’re worried about the thing catching on fire, stay on the latest macos you can and trust what it tells you in the uhh battery health section.

If you’re gonna use Linux then go ahead and replace the battery so that you’re not worrying about it failing miserably to communicate with the charge controller or battery itself and tell you when telhe thing is fucked and need replacing.