Very interesting thread…
Less than three years ago, I had the batteries replaced by Apple in my two 2015 MacBook Pros. (13” & 15”) $200 apiece, but I got new trackpads and keyboards, which I thought was a decent deal. Both had batteries swollen into nice looking pillows. (Apple’s price for replacement keyboards was significantly higher than that, which I found amusing, since it’s the exact same modification. The keyboard, trackpad, battery, and bottom case are all replaced as a single unit, regardless.)
Back then, I wondered whether keeping a MacBook plugged in 24/7 was bad for the batteries. I asked several “Geniuses”, even at different Apple Stores, and checked Apple’s website. Even asked phone support a couple different times to get more info. All agreed it would be no problem, and that keeping them plugged in wasn’t why my batteries had turned into balloons.
Now I’m back to square one. All the batteries are swollen into nice, comfy looking pillows again. This time, I did extensive research of Li-ion batteries specifically. (Not just MacBooks as before.) Discovered keeping them fully charged is very bad, and the longer they remain in that state, the more damage occurs. All research, over many years, have reached the same conclusions. Keeping them near 50% charged is ideal. Avoid going over 80% or much below ~40% if possible. This is why Apple products supposedly learn your habits, and charge to 80% until your patterns of use show you will need them soon, then they charge to 100%. At least that is according to Apple.
The Li-ion battery advice is hardly the only bad information I’ve gotten from Apple. Other experiences have included so much misinformation (and occasional total BS) that I’ve essentially given up asking them anything. Better off doing your own research than trusting Apple’s official statements. (Such a difference from when Steve Jobs ran the show–sigh.) This isn’t to say all Apple employees stick to the company line, but those who don’t soon find themselves unemployed.
One tip for anyone who, like me, uses their MacBook as a desktop computer; Plugged in 24/7. Get yourself a free little program called Charge Limiter, and set it to 50%. Works great so far for me! If the experts and their research are correct, I may be good for many years to come. The only reason I use a battery at all is because the models I own won’t even boot without a battery. I tried! I even tried disconnecting the batteries from the circuitboard, and plugging the circuitboard in, hoping to trick the computer. Nope!
