[dcb]

anyway, getting back to constructive and non presumptious things:

There may be another option that builds on Matts suggestion, that is both easy to hook up and not terribly expensive, and that is to utilize atmels I2C (or 2 wire) protocol, and make a bunch of attiny devices on that network that monitor the batteries (perhaps one attiny can monitor a pair of batteries or something). So each battery (or pair of batteries) gets a chip and get strung into the i2c network.

The floating grounds might be a problem though, if it were easy to make the attinys autorange in relation to ground, or if Matt has a chip suggesion for a floating ground adc that might prove helpful too.