Moto E 1st Generation unexpected battery problem

I bought the Moto E 1st generation phone 2 years back and it is doing well as of today. But when i full charge to 100%, and I'll monitor using DU battery saver. One day i was seeing videos in youtube and when the battery notified me 40%, I received an unexpected battery drop to 1% from 40%. And immediately, the phone shut downs. And now, it has been decreased. When it comes 20%, the phone immediately shuts off. Please let me know any suitable solutions for this problem?

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