I've had good service from several Cygolite Hotshot tail lights. One of them stopped holding a charge after less than two years, and that didn't seem right. I wrote to the company, and they said it would be $15 to replace the internal battery, so I said it's a deal. I sent in the light. They sent me a brand new light instead of fixing it. I'm satisfied!

LiIon batteries have a finite life, but overall, they're worth it.