1. Reset SMC. Choose the method for “If the battery is non-removable”.
https://support.apple.com/en-us/HT201295
Does this help?
2. Hold the option key down and click menu in the menu bar.
Choose “System Information” from the dropdown
Hardware > Power > Battery Information >Health Information > Condition
Does it say Condition: Normal?
3. About Mac notebook batteries: https://support.apple.com/en-us/HT204054