Battery - Shut down or sleep an MBP

There are two factors that govern the life of a battery:

• Age
• Charge Cycles

The biggest factor is age. Math Finds Top Culprit as Lithium Batteries Age

...a battery ages, or degrades, whether it is sitting on a shelf or in use. The main cause of lithium-ion battery aging is the continuous formation of the solid electrolyte interphase (SEI) layer in the battery. The SEI layer must form for the battery to work because it controls the amount of chemical reactions that occur in the battery.

The next is cycle count. A complete discharge and recharge is one cycle. A 20% discharge 5 times is one cycle, a 5% discharge 20 times is one cycle.

Whether that cycle takes a half day, a full day or a week all depends on how you use it; sleeping will put a very, small draw on your battery versus being off but the difference is almost negligible - I am assuming that you are not sleeping your MacBook for weeks at a time.

Even when you keep your MBP plugged in, you are reducing the per day cycle count; however you are not eliminating it.

Why does cycle count matter? From the article again...

As the battery is continually used, however, small-scale side reactions build up at the SEI layer, which decreases battery capacity—how much of a charge the battery can hold.

Bottom line

It's doesn't matter. You can expect to replace your battery somewhere between year 3 and 4. Can you get longer? Yes. Can it be shorter? Yes. It's tough to know exactly when, but choosing "sleep" over "power off" isn't going to make a big difference.

There are many factors/measures when it comes to batteries, and often people get confused by the various terms and what they mean. For example, Battery life is the amount of time it will last before it needs recharging, while Battery lifespan refers to the overall life of your battery before it needs replacing.

There are many other terms/factors and this type of confusion leads to debate/argument about what is best practice.

However, in the event this question isn't closed because it's primarily opinion-based, the best advice I can offer you and other readers is to familiarise yourself with what Apple says about their batteries - this removes the 'opinion' out of it!

To do this go to: http://www.apple.com/batteries/