I doubt you're really at 100%... if you go to "Apple menu > About This Mac > System Report > Power > Battery Information" you can look at "Health Information >

I doubt you're really at 100%... if you go to "Apple menu > About This Mac > System Report > Power > Battery Information" you can look at "Health Information > Cycle Count" and see how many cycles you've been through... see "Cycle Count Limits" at https://support.apple.com/en-us/HT201585 https://support.apple.com/en-us/HT201585 for expected lifetime. You could also look at "Charge information > Full Charge Capacity (mAh)" and compare that to whatever the original capacity was for that model.