There are services like this where you can exchange your Airpods for ones with replaced batteries! Note that I've never done it and can't vouch for the quality. I just read about it on HN once.

https://www.theswapclub.com/collections/airpod-swaps

I‘ve used a service like this to replace the battteries of my Airpods Gen 1. They are now again like the first day I had them.

And how much larger would they be?

That's an interesting question, and I'd like an honest answer to that.

We've heard the same argument about phones, and my old Galaxy S5 with a user-replaceable battery was a whopping 0.5 mm thicker than an iPhone 13 mini. That's the width of a mechanical pencil lead. They're both water-resistant, too.

.5 inches and heavier for AirPods would make a huge difference ergonomically.

I said 0.5 millimeters. 0.5 inches is freaking huge, that's 1.25 cm. None of my smartphones have been that thick, let alone having that much of a difference.

According to google, 0.5 mm = 0.019685 in