Airpods die at 50%

My second-generation AirPods die at 50%. Well, only the left AirPod. The airpodcase is still charging normally and it shows that my AirPods are being charged on my phone. However, my left airpod dies at 50% while the right one is completely fine. Is this a software malfunction and or is there any way I can fix this? Or are my AirPods just too old? Thanks a lot in advance!