Swollen means the battery has degraded and increased in size to the point it cannot be removed. This is considered a safety hazard. So Logitech will replace the entire remote even though it is out of warranty.

Remotes don't become sluggish due to wear or age. Something else is causing that.

Replace it for whatever reason you want. I was just suggesting the free option in case you weren't aware. If you like spending $300 on remotes, knock yourself out.