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在2017年6月，Apple更新了13寸的MacBookair，他换上了更新更好的Intel Core i5处理器，让性能和电池续航时间提高。

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Replacement Battery Suddenly Drops from 40% to 20% after I reset SMC.

My MBA 2017 got a Service Recommended for the battery 2 months ago and I ordered a replacement battery off iFixIt. Once it arrived, I installed it without issue and calibrated it as instructed but the battery was dropping 1% every 2-3 minutes with just Safari open at half brightness. I tried resetting the SMC but it would then rapidly drop to below 20% from around 40% and would drain even faster after that. This continued for a few cycles so I contacted Support and they sent a new battery as they said it looked like a bad battery to them.

I installed the new battery a week ago when it arrived and did the calibration. It dropped at the same 1% every 2-3 minutes rate all the way from 100-0% and I decided to reset the SMC to see if that improved battery life. Unfortunately, the sudden drop from 40 to 20 problem reappeared. I reset the SMC again but the problem persists. Did I get another bad battery once from iFixIt? (Coconut Battery shown below for reference) Should I not have even touched the SMC? Should I re-calibrate the battery after the SMC reset? Any suggestions would be appreciated.

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Update (03/27/24)

UPDATE: Per @danj 's request, here's CoconutBattery after it charged for 8 hours.

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Update (03/28/24)

Here's CoconutBattery after 4 hours off being off the charger and not using the MacBook

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Update (03/29/24)

Seems charging it to 100% and leaving it there for several hours did the trick as the battery did not suddenly drop at 40% and has held on with a steady discharge rate down to 25% as I write this now. I do wish the charge would last me longer (YouTube knocks off 1% every 1.5-2 minutes whereas Netflix and casual browsing on Safari gets me 3-4 minutes per percent point) but for a nearly 7 year old machine and third party battery replacement, I'll likely just have to deal with that and the 5 hours of screen time I've gotten in so far on this cycle is still longer than most Windows laptops last on battery.

One other thing I didn't mention initially is that after calibration I was only charging back up to 70-80% as I read that lithium-ion battery health is best preserved between cycles of 20-80%. That is also when the issue started so I'm now leaning towards that being the culprit instead of the SMC. Thanks @danj for your help!

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What are you using for a charger and cable?

Looking at CoconutBattery shows the battery is charging, just not fully charged with a somewhat high temp.

Let it charge a good 8 hours, take a fresh snapshot, then if you can, don’t use the system for four hours, then take one more snapshot. Posting then here so we can see.

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I'm using a 45W MagSafe 2 from Apple. My original that came with the Mac stopped working in October so this one isn't that old. Should I leave it plugged in for 8 hours once it hits 100% or just 8 hours plugged in even if part of that is while it's actually charging up to 100?

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@spencerschmudde - The battery should be fully charged after 8 hours. When you run CoconutBattery you should see that. Then shutting down the system with the charger disconnected should stay at this level of charge for 4 hours. I’m trying to see if we have a partial short which is running down the battery.

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@danj - Gotcha. Thanks for clarifying. Both battery screenshots are up now.

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@spencerschmudde - Well the battery appears to be holding its charge. I assume you are using the system now is it running OK now?

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@danj - It seems fine for now. I’ll use it as normal and see if it suddenly drops when it gets around 40% again. Hopefully it doesn’t. Will update later.

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