AirPod low battery reported on Zoom and FaceBook calls

When I use my Apple AirPods (1st generation, A1523) on Zoom and FaceTime calls on my MacBook Pro I’ve been getting pop-up warnings that the AirPod batteries are down to 10% even after fully charging them beforehand. So I have to scramble to find my wired EarPods to complete the calls.

But when I put the AirPods back in the case my phone says they’re 99% charged! What’s up with that? Why am I getting the low battery warnings? Or is my phone reading the battery charge incorrectly?