Asus laptop shuts down when unplugged

My laptop [Asus X541U running Windows 10] started to shutdown randomly when it is on battery, after a couples of weeks it completely stopped working on battery.

I took it to someone who disassembled the laptop and tested the battery which was working fine nd cleaned the laptop a bit then the laptop worked fine with battery and without random shutdowns.

Now after 3 months the problem is back again the laptop started to shutdown randomly when it is unplugged and I am afraid it will completely stop working on battery after couple of days.

What can possibly be the problem? I know is that the problem not in the battery.

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