In circuit 2S Lithium Charging
There are a number of LiIon charger ICs that claim to adequately manage the charging of two LiIon cells in series with no centre tap connection to the battery.

The below referenced Microchip IC is an example - their presumption seems to be that balancing for a 2sS battery is not needed. 

This IC was chosen on the basis of meeting 2S spec, being in stock at Digikey and being about their cheapest offering - not always the optimum way to choose ICs :-) 

The IC is the MCP73841/2/3/4 - Datasheet here.   

This IC uses an external MOSFET for charging control and a 100 mV sense resistor with 100 mV drop at target current. 1A example circuits are given but a 100 mA or 10A charger could be equally well implemented. 

Only claimed differences are xxx1 &amp; 2 have thermal monitor and 3/4 do not, and 1 &amp; 2 are for 1 x LiIon cell and 3/4 are for dual LiIon cells.

No obvious difference in general functionality is present between the 1 &amp; 2 cell versions.

A reasonably good skim through the datasheet does not turn up any mention of cell balancing. Microchip almost always seem to 'know their stuff' - their presumption seems to be that balancing for a 2sS battery is not needed.