After four years of faithfully annoying motorists my favorite bike light ceased to take a charge. Not wanting to throw it away, I set about finding a way to repair it.
Having carefully pried off the face plate and popped open the water seal in the vice of knowledge, I discovered a rather sad-looking 603131 lithium cell. Finding a replacement of the same size proved to be an unviable option with minimum orders of 8000 units. Fortunately, very slightly smaller 603030 cells are readily available on eBay for a few dollars.