MacBook only works when plugged in???

You should visit an Authorized Apple Service Provider, to get the MacBook checked. Maybe the battery got damaged. Depleting a lithium battery completely can make the battery unusable.

Mac Repair - Official Apple Support

There is the possibility that when you first fired it up, that you didn't completely shut it down, in which case, the battery power has been depleted.

It's generally a good idea to charge the battery to a minimum 85% before the MacBook will fire up without the charger.

There's also the possibility that the battery has been completely drained.

Next time you power up with the charger, go into 'About this Mac' from the dropdown below the Apple logo.

Go to System Report>Power to see Battery Health. This will tell you the general condition of your battery and whether it needs to be replaced.

[Edited by Moderator]

Panda988 wrote:

Hi, I checked in the system report and it says that the battery condition is normal. Now what?

Then keep an eye on it. It could have been an issue with the connection between the battery and the logic board, although it's usually pressed in by the case. I've actually had a battery that flip flopped between service now and normal. That one was probably corrupted after a thermal shutdown, and for some time it was reporting negative capacity, although it still powered the Mac. Eventually it swelled, but that was back when swelling didn't damage the case or logic board.

try to update software but if its updated their is non other option just take it to service center they only can help you because in apple product their is nothing to do only service center can help us.

sapper wrote:

There is the possibility that when you first fired it up, that you didn't completely shut it down, in which case, the battery power has been depleted.

It's generally a good idea to charge the battery to a minimum 85% before the MacBook will fire up without the charger.

There's also the possibility that the battery has been completely drained.

Next time you power up with the charger, go into 'About this Mac' from the dropdown below the Apple logo.

Go to System Report>Power to see Battery Health. This will tell you the general condition of your battery and whether it needs to be replaced.

A month after it's been depleted to "0%" shouldn't necessarily kill the battery. However, we haven't gotten any details about whether or not it had already been turned on or anything else specific. Once the device shuts down it shuts down and doesn't really draw much from the battery. It might take months before it reaches "deep discharge" through self discharge, although temperature would make a difference.

I'm wondering if the battery was already dead (or nearly so) when the OP got it.