At the moment, I believe the ESS works with groups of four Li-ion cells for the purposes of charge monitoring and balancing. In this paper published in September, Texas Instruments seem to be suggesting that larger group sizes are possible.
"Battery fuel gauging applications requiring five- to eight-series cells may not have an obvious solution. While fully functional solutions are anticipated in the future, currently available chipsets tend to address end-products where four-series cells are the maximum. This report presents an inexpensive solution, using the bq20z80 fuel gauge."
http://focus.ti.com/analog/docs/techdocsabstract.tsp?familyId=413&abstractName=slua435
"Battery fuel gauging applications requiring five- to eight-series cells may not have an obvious solution. While fully functional solutions are anticipated in the future, currently available chipsets tend to address end-products where four-series cells are the maximum. This report presents an inexpensive solution, using the bq20z80 fuel gauge."
http://focus.ti.com/analog/docs/techdocsabstract.tsp?familyId=413&abstractName=slua435