Try these steps first before buying a new Mac.
1. Reset SMC: How to reset the SMC of your Mac - Apple Support Choose the appropriate method.
Quote:
Resetting the system management controller (SMC) can resolve certain issues related to power, battery, fans,
and other features.
2. Startup in Safe Mode. https://support.apple.com/guide/mac-help/start-up-your-mac-in-safe-mode-mh21245/mac.
Quote:
It also does a basic check of your startup disk, similar to using First Aid in Disk Utility.
And it deletes some system caches, including font caches and
the kernel cache, which are automatically created again as needed.
3. Battery Management.
How battery health management helps
The battery health management feature in macOS 10.15.5 is designed to improve your battery's lifespan
by reducing the rate at which it chemically ages.
The feature does this by monitoring your battery's temperature history and its charging patterns.
Based on the measurements that it collects, battery health management
may reduce your battery's maximum charge when in this mode.
This happens as needed to ensure that your battery charges to a level that's optimized for your usage
—reducing wear on the battery, and slowing its chemical aging.
Battery health management also uses the measurements to calculate when your battery needs service.
https://support.apple.com/en-us/HT211094?cid=mc-ols-energy_saver-article_ht211094-macos_ui-04022020'
4. Section: Tips for MacBooks
https://www.apple.com/uk/batteries/maximizing-performance/
5. Monitor your Mac notebook computer’s battery