Since many battery expert believe 100 percent battery would hurt battery's life.So m y theory is, when you use like 45w charger which has lower than apple's original one( 96 power), you can keep your mac's power very slowly increase from 40% to 80%. And in this time, it won't count your battery circle and also keep the battery around 40 to 80. Is it good for the battery life?

My concern is when you use a program which need a lot of power, the 45W charger may not be able to charge the MAC normally, and keep the MAC power down. Will this damage the battery?

I need to use macbook pro for a long time a day, because I don't have a desktop, and I don't want to damage the battery. Is it a good way to use a small power to charger mac?

4 Answers 4


If you have a weaker charger charging the device and the device is draining power more than the output of the charger, it could cause damage to the battery or break the battery because of heat. Some devices may draw power directly from the battery if the charger does not produce enough power. This causes a lot of heat generation. In addition, the charger could break because it is trying to meet the power demand from the laptop. A good rule of thumb is to avoid using the device when you are charging it. It is highly recommended to always use a charger that is designed for the laptop or battery. (In this case, a standard issued authentic Apple macbook charger)

Essentially, it is important to try to avoid excess heat generation because it could cause irreparable damages to the battery, device and charger. If you are concerned about what battery percentage you should leave you laptop at, I would suggest trying to keep the battery percentage always above 30-50%. Another user on the mac forums suggested that it is good to leave the battery at 75% once a month to keep the battery exercised. This method helps the battery to maintain overall storage power capacity.

Here are a few other things to keep in mind:

  1. Try to avoid using the device when you are charging it because the battery or charger could get hot. Heat is known to degrade the life of a battery and has been studied extensively. A study in science direct says Lithium Ion Batteries should stay within −20 °C ~ 60 °C (-4°F ~ 140°F). If the a Lithium Ion Battery is exposed to temperatures outside of those ranges, the life and quality of that battery will degrade.
  2. When charging a device, the device may be drawing power from the battery while charging the device. This will cause the battery to heat up.
  3. Depending on the device, the device may be drawing power directly from the charger. This will cause the charger to heat up a lot.
  4. Most modern macbooks have some sort of built in functionality that will drain and recharge the lithium ion battery when at 100%. So, there is no need to worry about damaging the battery.

Apple does provide some official guidelines that Apple users should follow:

  1. Avoid hot ambient temperatures. An ideal range would be from 16°C to 22°C (62°F to 72°F). Hot temperatures are known to permanently damage battery capacity. Cold temperatures causes a temporary decrease in battery life.
  2. The built-in software will limit charging above 80% when the recommended battery temperatures are exceeded.
  3. Remove cases when charging. Leaving it in a case causes more heat generation.
  4. For long term storage, do not fully charge or fully discharge your device's battery. 50% is an ideal percentage. If you fully discharge the device for long term storage, the battery could be rendered unchargeable. If you fully charge the device for long term storage, the battery may end up having shorter battery life.
  5. For long term storage, make sure the device is powered down and leave it in a moisture-free environment that's less than 32°C (90°F).
  6. For Long term storage, if you plan to store more than 6 months, charge it to 50% every six months.

I hope this information help!

  • Thank you! appreciate it!
    – iTvX
    Nov 24, 2019 at 2:13

So long as the AC adapter is an Apple adapter, you will not damage the battery with the lower power. However, if you have an application that needs the higher power use the original adapter to make sure the machine works properly under higher load.


The wattage of the charger does not influence whether it can charge the battery to 100% or some other value. It will either just charge more slowly (which in general may be better for the battery than quick-charging), or as some laptops do, refuse to charge at all (e.g. Dell laptops requiring 90W charger do not charge if a 65W charger is inserted, although they may run with such charger in a safemode with the lowest CPU frequency etc.)

Li-ion and Li-Pol battery cells found in laptops, phones etc. indeed suffer if they are permanently charged to 100 % capacity. Some laptop brands offers tools to limit charging to a lower percentage exactly to prolong battery life (Lenovo in its Thinkpads via Vantage SW, some Fujitsu Lifebooks, etc.) If the vendor does (Apple) does not offer any tool to reduce max charging to less than 100 % it does not make much sense to try to somehow workaround it. Generally it is still better to have the battery charged and run most of the time on the AC than to have it use it mostly on battery and charge it then, which eats the recharging cycles.

There are other factors influencing Li-ion battery life, such as the current draw (rendering video/playing games while on battery damages it quicker than just writing text in Word), temperature (high temperatures above 60°C really hurt Li-ion cells), and keeping the battery totally depleted (which can eventually irreversibly destroy the cells, and the circuitry prevents any future charging which would be dangerous).

  • Thank you! appreciate it!
    – iTvX
    Nov 24, 2019 at 2:14

Elam and Martin both have a lot of good information in there, but I have to disagree with some points. First, (as both have partially or fully covered), things that are bad, roughly worst first:

  • Charging fast *
  • Charging while hot
  • Hovering at full charge
  • Getting/being very hot
  • Cycling the battery (charging then discharging)
  • Discharging all the way to zero (not very bad for Li-Ion)

(*) Caveat: if you're charging slower than 0-to-100 in 1 hour (1C), going much slower isn't a huge difference. If you're charging faster than 0-to-100 in 30m (2C), you're putting a LOT of stress on the battery)

In general, your intuition is quite right: charging slower will wear the battery less, and heat it up less as well. Modern laptops in general, and MacBooks in particular, are specifically designed to draw power from both the adapter and battery under high usage. The thermal design limits average power, and therefore the max power a charger needs to provide, but the components can draw much much more power for brief periods if needed, until they heat up. That's why processors have a "turbo boost" frequency. A MBP with its battery removed will actually throttle its performance specifically to make sure no spikes exceed what the adapter alone can handle.

All of that to say, using a less powerful charger is, indeed, a good idea, until the point that your workload is enough to drain your battery dead even while plugged in. But it's also probably not a huge deal.

Charging while hot is a problem, but it's SUCH a problem that there's a ton of smarts built in to manage it - it's actually a UL requirement.

Hovering at a full charge, I think, is probably the worst battery offense that consumer devices frequently commit. Apple seems to (finally) agree, and is actually introducing Battery Health Management to address this in Catalina 10.15.5.

If you want a little more control over peak charging level and you're on Catalina, the following two projects are options: https://github.com/davidwernhart/AlDente https://github.com/sicreative/BatteryStatusShow

If you're not on Catalina, or you're an Alfred user, I put together a workflow for this. Download link right after the first screenshot in this post, with a lot of additional info as well: https://www.alexwhittemore.com/controlling-macbook-pro-charging-cap-with-alfred/

Finally, I take exception to "A good rule of thumb is to avoid using the device when you are charging it" - if you were to do that, 100% of your usage would contribute to cycling the battery, and you'd probably wear it quite a bit faster than if you operated on shore power regularly.

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