Does overcharging a MacBook degrade its life?
All Macs cease charging and let you know this by changing the "orange" LED in the charging cable to "green" when the battery is topped off and you are merely running the Mac - not charging it.

The question you ask would be more precisely worded - what harm is it in keeping the battery constantly and always topped off to full?



Your early 2011 13" MacBook Pro has a lithium ion battery. Luckily, lithium ion batteries have an internal circuit to prevent the battery from being charged over 100%. There is a very slight chance that something can go wrong with the charging mechanism in the laptop, which would cause the battery to overcharge, but I wouldn't be concerned with that.

Years back, laptop batteries were made from nickel-cadmium or nickel metal hydride. It was recommended that these batteries were regularly fully discharged then fully charged so they'd continue to hold a full charge, though even following these practices they would eventually lose capacity.

Apple still recommends that you fully discharge your battery monthly, and never store your laptop with a charge below 50% for an extended period of time. In short, it's perfectly acceptable to leave your laptop plugged in while it's in use but let it fully discharge once a month for optimal battery health.