Einstein and car batteries: A spark of genius?

Sez the Economist:

For, according to Dr Pyykko’s calculations, relativity explains why tin batteries do not work, but lead ones do.

His chain of reasoning goes like this. Lead, being heavier than tin, has more protons in its nucleus (82, against tin’s 50). That means its nucleus has a stronger positive charge and that, in turn, means the electrons orbiting the nucleus are more attracted to it and travel faster, at roughly 60% of the speed of light, compared with 35% for the electrons orbiting a tin atom…

If the problem isn’t immeadiately obvious to you, pause a moment before proceeding over the fold.