Greetings, gkdxb!
Thanks for reaching out to the Apple Support Communities! It sounds like you have an issue with your MacBook Pro not charging beyond 80-81% since replacing the battery. Check out this article to Charge the MacBook Pro battery:
"Optimized Battery Charging helps to reduce the wear on your battery and improve its lifespan by learning your daily charging routine. It delays charging the battery past 80% when it predicts that you’ll be plugged in for an extended period of time, and aims to charge the battery before you unplug. You can change this option in Battery preferences."
Have you noticed the issue if you close the screen and leave the MacBook charging for an extended period of time?
We also suggest checking out this article About battery health management in Mac notebooks:
"While battery health management benefits your battery's long-term lifespan, it can also reduce the amount of time your Mac runs on one battery charge when capacity limits are applied. If your priority is making your Mac notebook last as long as possible before recharging, you can turn the feature off."
If you still have an issue after turning the battery health management feature off, we suggest checking out this article to Get help with your Mac notebook battery.
Let us know the results and have a great day!