Using MCP73213 for charging two Lithium ion batteries connected in series
It depends on your application.  If the batteries are charged slowly (&lt;0.5C or so), discharged slowly (&lt;0.5C or so) and operated at normal temperatures, balance is usually not a huge issue.  

That said, it might be easier to just use a single cell battery and a switching boost converter to generate the 5V rail.