Theoretically there is no problem. Regardless of how many cells there are, DS2788 only measures a single cell average voltage of the battery. However, there is one problem practically: finding a high voltage LDO to convert battery input voltage into the 4.5V used for power supply voltage for DS2788, and has very low static power consumption. This is because DS2788 cannot measure the current consumed by LDO itself. When the LDO needs to supply a significant load (e.g LED), the power consumption by LDO may be significant. The power dissipation of LDO itself needs to be taken into consideration, and the MOSFET for external voltage division must also support higher voltage. As long as these requirements are met, there is no problem in supporting more batteries in series.