Battery consumption while MacBook connected to charger

Question

I want to ask about energy consumption from the battery and wear-and-tear while the MacBook is connected to electricity socket / charger.

As we know, laptops can work both on a battery and on electricity.

First, I'd like to know if when the MacBook is connected to the household electricity with charger, there is still wear-and-tear on the battery, even if it's fully charged? If so, is it minimal wear and tear? If, for example, the battery was completely broken or non-existent, could the laptop still work with a direct connection to electricity (so receiving the electric current from charger and not from battery)? I'd appreciate an answer specifically for the latest Apple MacBook models, for example those with the M1-M2 processors (yet it's also interesting for Intel models). I can learn from this answer (from 2018) that there's a battery usage, but not sure if it is for the case of 100%-charged one, and also if it's actual for 2022 models and USB-C.

Second, as you know, we can connect electronic devices (eg smartphone, USB fan, etc.) to the USB-C ports of the MacBook and the laptop will charge those devices. When the laptop itself is connected to the home electrical outlet, will the charging of these devices be carried out through the battery (thus potentially causing wear and tear) or does the motherboard transfer the current directly to these devices and skip the battery? Whether the battery is full or not

P.S. Note, the main goal of this question for me is to know if there is degradation to the battery health if I charge my iPhone through the laptop, or on a daily basis there is probably no significant difference if I charge it directly to the household electricity, compared to charging through the laptop which is physically more convenient for me. However, I would appreciate a direct answer to the questions above just as I asked them

Answer 1

To be fair, you ask several questions in one thread, which might create reference problems later. I see you are new, so I will answer your question; however, one suggestion for the future is, please post separate questions in separate threads.

if when the MacBook is connected to the household electricity with charger, there is still wear-and-tear on the battery, even if it's fully charged?

Yes. But the wear-and-tear comes not from the power adapter supplying power to the battery, but from the fact that the battery is 100% charged. The more charged a battery is, the faster it wears out. For people concerned with battery longevity, there are computers that stay charged at around 60%, with the possibility of pushing a button to charge to 100% when you anticipate needing that extra charge somewhere.

What I do to avoid wear-and-tear on the battery is, to get the battery discharged to ~15%, and then use a non-PD charger (PD = Power Delivery, a USB standard that Apple uses to charge). The non-PD charger keeps the MacBook running without charging the battery; as such, my battery is almost 12 years old, and still running strong.

Also, there is a question Can I tell my Mac to charge to 80% only? that details other, more automated ways to avoid having the battery charged to 100%.

If, for example, the battery was completely broken or non-existent, could the laptop still work with a direct connection to electricity (so receiving the electric current from charger and not from battery)?

Since you're asking only about the latest models, yes. But there has to be smart circuitry that internally disconnects the battery; in sufficiently old models this is not possible.

will the charging of these devices be carried out through the battery (thus potentially causing wear and tear)

The answer is No. This is due actually not to the Motherboard transferring the current to the devices, but rather this is a direct electrical principle, that electricity flows down the path of the least resistance. So if there is a device connected to any laptop, the electricity will flow down to this device before even reaching the battery. (The only exception is if your computer and charging consumptions use more watts than the adapter provides -- but this should only happen if you are using a weak non-standard charger).

P.S. When I was small, I was asking these exact same questions. Welcome to this community!