Is MacBook Pro overheating bad for the battery?

Hello milic22,

Welcome to Apple Support Communities. We're glad you're here, and thank you for posting.

You've asked several questions about the Mac battery relative to battery health, cycle count, and how increased heat may impact the battery. We'll be glad to share a few tips to guide you and answer your questions.

• First, we recommend reviewing this informative guide to learn more About Mac notebook batteries.
• Next, open the  Menu > About this Mac > System Report > Power where you can view the Health Information, including the Cycle Count and Condition.
• Open this link to learn how to Keep your Mac notebook within acceptable operating temperatures.
• Lastly, please tell us where you were viewing 89% for the Battery Health?

We look forward to hearing back at your convenience.

All the best!

If i don't do something it will be under 80% in the first year, at around 225 cycles.

My understanding is also that 1000 cycles should be around 80% battery health.

Decline in battery health is not linear. It's normal for a new battery to drop at first then stabilize. My 2017 15" MBP dropped to ~90% health after about a hundred cycles. I've got 301 cycles on it now, and the health is 91%.