Magicshine makes one model (Alty 2000) with a removable battery pack. They used to sell a model with a removable "raw" 18650 cell, so you didn't need to buy a proprietary product from them. As far as I know, this is the only self-contained light with a swappable battery pack. There are a lot of bikes with separate battery packs where you could obviously swap packs. There are some lights that can operate while hooked up to an external USB battery pack, but this isn't well-documented. Not all do.
300 lumen doesn't sound like enough to me, but in any case, lumen is a rough stand-in for the more relevant metric, which is how far your light throws its beam, and whether you'll outrun that at your typical speed. Some beams are more diffuse, some more focused. I'm guessing that for riding through a forest, you'd want a little more diffusion than on the road.