@georgetakei it happens to me all the time. It is usually:

1. When you are talking on a call the ios device picks one earpod to be the main mic. That one drains power a lot more quickly

2. Frequently one of my airpods doesn’t make good contact in the case to charge, so it never gets a full charge. I have airpod pros, and for me it is my right

It can of course be both together