One of the articles I read in a highly technical battery forum, was that newer battery packs will degrade gracefully.

What does it mean? Since each individual cell is very low voltage (from 1.25 fully charged to 0.9 volt discharged, typically 1.1 volts under load) it takes hundreds of cells in series to achieve the voltage required by the battery pack. The keyword here is in series..... just like your christmas tree lights...all it takes is a single burnt out bulb, for the string to become useless. Same with series battery packs... a single defective cell renders the pack useless.

So what battery manufacturers are researching is into ways to find out the cell that has gone dead, and just bypass it completely. The voltage loss is usually quite low, and the pack can tolerate a few individual cell failures before being rendered useless.

Now we are talking 150,000+ miles battery packs.