How do you rebuild an electric bicycycle battery?

Electric bicycle batteries are mostly proprietary and are expensive--often the most expensive part of the e-bike, yet lithium ion cells from major manufactures are much less expensive. A bike battery should reasonably last 2-4 years depending on how they are charged and usage. You should not have to replace a $1,000 battery after two years, if there is a repair option out there. iFixit would seem to be an ideal forum for this with the increased interest in electric bikes for commuting, pleasure and adventure.