Apple Battery Health Dropped 10% within 2 months

AffanTariq wrote:

I've been using my mac M1 2021 that I bought in the beginning of 2023 and started using more often Jan 2024, it recently dropped battery health from 100% to 90% within a span of just a couple of months. I don't think that

seems to be normal. I am using a local extension cord to charge my mac and use my screen plug at the same time. Could that be the reason?

Normal.

extension cord— absolutely not related.

I would just use it as you see fit. It is not necessarily a linear progression downward with Optimize Battery charging.

You do not have to micro-manage battery charging

The rule of thumb—if you are near the mains leave it plugged in, if you need the portability then run on the battery only—this is how you help optimize your battery charging and extend the working life of your battery by reducing the cycle count.

About BHM battery health management M1/M2/M3 SoC

About battery health management in Mac notebooks - Apple Support

Please note:

≤ 80% maximum capacity is when Apple suggests the battery is eligible for replacement

You mentioned you were not using the laptop very much for the first year. Did you let the battery drain to 0% for any extended periods? If so, then you may have damaged the battery which could be part of the problem.

However, like @leroydouglas mentions, this 10% drop of the Maximum Capacity is also not unusual especially for a year old computer (assuming it was not made earlier than 2023 and was sitting around in a warehouse). See my other post where I explain how these Apple Lithium Batteries behave in regard to the Maximum Capacity value that Apple only recently started displaying to people in macOS Ventura:

Battery Health draining fast -- Explanation by HWTech- Apple Community