My airpods ran out of battery even thought it was full.

So recently, my airpods started going out of battery on either side even though i've fully charged it. And then when i put the one on the case, it started charging for a few seconds and then instantly full. This problem persists and changing left and right. And when i put it back on my ear, a few minutes later the other side that i did not put in the case suddenly are out of battery.

Is it battery problem? or is it just the age of the airpods? i've had it for around 4 years i think. But i think airpods should last longer than that.