MacBook battery going down while plugged in: why and what to check
Why a MacBook loses charge while connected to power, from a low watt charger to a heavy workload, and how to read the charger's wattage on your Mac.
Why is my MacBook losing battery while charging?
Because the workload draws more than the adapter supplies. A 20 W phone charger, a low quality cable or a hub that splits power can deliver less than a busy Mac uses, so the battery makes up the difference.
How do I check my charger's wattage on a Mac?
pmset -g adapterIt shows the wattage, voltage and current the Mac negotiated. If it is far below the adapter that came with the Mac, change the charger or the cable.
What else makes a Mac drain while plugged in?
Sustained heavy work such as exports, games or a stuck process at high CPU. Activity Monitor's CPU tab shows it: find what is using the CPU.
Common questions
Can a MacBook drain with the charger in?
Yes, when it uses more power than the charger supplies, typically with a phone charger, a weak cable or a heavy workload.
How many watts does my MacBook charger give?
Run pmset -g adapter in Terminal. It shows the negotiated wattage, voltage and current.