Hello and welcome to Apple Support Communities ruman112,
We see that you're having an issue when the battery in the AirPods die, then it disconnects the phone call that you're on. We know that it is important to not have your calls disconnect, and we'd be happy to help.
What you're experiencing is not expected behavior with your AirPods and your iPhone. The call should continue through your iPhone, or if you're in your vehicle and using CarPlay, it could continue there as well. Since this is not expected behavior, we'd like to have you reset your AirPods, and then test to see if the issue remains.
Reset your AirPods
If the issue continues after resetting the AirPods, please respond back with some more details. Are you noticing this happening when you are in a specific area? Does this happen on every call? Is this something that just recently started happening, or have you always had this issue since purchasing your AirPods?
We look forward to hearing back from you.
Have great day!