Should you leave your MacBook plugged in all the time?

This is the question we get most, so let’s get the short answer out of the way: it isn’t the cable that wears your battery out, it’s the state the cable keeps it in. A MacBook parked on a desk all day sits at 100% and runs a little warm. That combination is exactly what ages a lithium-ion cell fastest.

Two things wear a battery out

The first is cycle aging: every full charge uses up a slice of the battery’s life. That’s the number everyone knows, and it’s the less worrying of the two — a MacBook is built for roughly a thousand cycles.

The second is calendar aging: the battery degrades just by existing, and it degrades much faster when it’s held at a high state of charge — faster still when it’s warm. This is what hits always-plugged machines, and almost nobody talks about it.

Why permanent 100% is the worst case

At full charge, cell voltage is at its peak, and the side reactions that eat the electrolyte run faster there. Holding that state for months costs you more capacity than the handful of cycles you’d have spent by simply working on battery.

Now add heat. A plugged-in Mac that’s compiling, exporting video or running a couple of VMs gets hot, and the battery gets hot with it. High charge plus high temperature is the single most damaging combination there is.

What macOS already does — and where it stops

Apple knows all this. Optimized charging learns your routine and holds off on the last 20% until around the time you normally unplug, and recent macOS versions add an 80% limit.

That’s genuinely useful, with two catches. Optimized charging is a prediction, so it gets your schedule wrong the week your schedule changes. And the built-in limit stops at 80% — you can’t go lower, and you can’t bring a battery that’s already full back down.

What to actually do

• Staying plugged in is fine as long as the charge is capped. It’s permanent 100% you want to avoid, not the cable.
• Don’t run full cycles “to condition the battery.” That habit comes from nickel cells and it backfires here.
• Watch temperature more than percentage. A machine that runs hot while charging ages fast.
• Go back to 100% the night before you travel, then drop back down. The occasional exception costs almost nothing.

That’s exactly what Cooked does: a limit you set one percent at a time, well below Apple’s 80% floor, active discharge so a full battery comes back down without unplugging, and health and cell temperature in plain sight. Free forever, no account — the hot-cell pause and the history are in Pro, $19 once.