How to avoid battery of Macbook worn-out

Use it on AC power when available. Leave it plugged in when idle, it will never over-charge.

Use it on battery when AC power is not available.

For long battery life, do not store it less than half charged for any appreciable amount of time, and do not allow it to get HOT, such as in a hot car in the summer.

Hello an124,

Thank you for using Apple Support Communities! I understand that you're wanting to know if your MacBook Pro should be connected to a charger when one is available to help maximize battery capacity. I would be happy to help provide more information.

The lithium battery in your Mac is designed to count a full charge cycle only when it has discharged 100% of the batteries total capacity. From the resource below, "For example, you could use half of your notebook's charge in one day, and then recharge it fully. If you did the same thing the next day, it would count as one charge cycle, not two. In this way, it might take several days to complete a cycle."

Determine battery cycle count for Mac notebooks - Apple Support

For your specific Mac, the Maximum Cycle Count is 1000. Connecting the Mac to a power supply when the battery is not discharged would not extend the battery life with how the charge cycle is designed to work. You can learn more about this feature, and tips to help maximize battery life and lifespan here:

• Batteries - Why Lithium-ion? - Apple
• Batteries - Maximizing Performance - Apple

Take care.

I connect to a power supply whenever it is convenient. In the example provided by i_rina above, if you discharge the battery 50% on day one then do the same thing on day two that would represent i charge cycle. If you leave your computer plugged in over the same two days and use the computer the same as in the previous example, there would be zero charge cycles over the same two day period.

No, there is not. Be aware though that these batteries can fail even if their cycle count is still relatively low. In that case, they can swell and damage other parts, so simply not using it may not avoid that. Normally though they are really long lasting.