>But Koslowski says those old batteries could also become part of a robust secondary market. They could, for instance, store energy generated by home solar grids, which can make use of less-than-full strength cells because they don’t have to go anywhere.

Is that how the degradation curve of LiIon batteries goes? My experience with them in consumer electronics has been that they seem to drop capacity about linearly for a while, and then suddenly there's a massive drop-off and the battery becomes more of a brick than anything.