polymer li-ion battery monitoring and under-voltage protection

There are a number of manufacturers out there producing porotection chips for 1 through 4 cell stacks, but thye were VERY hard for us to locate two years back.

One of the key roles of the protection module in multi-cell configurations is to guard against differences in cell voltage. When these differences appear, the result of a voltage divider approach is that the lower voltage cells discharge further than the "average" represented by the divider. Similarly, on charge the CC->CV transition and termination conditions will be met with (at least) one cell at a higher than desired potential. Both are potentially dangerous situations. Use a 3-cell protection chip for a 3-cell string.