As long as cost is not an utterly compelling factor, and it's not 
likely to be:     Choose a battery that, regardless of voltage, and 
given physical and mechanical constraints, best meets *your* needs for 
energy capacity, rechargeability, self discharge rate etc. THEN choose 
a suitable available modern power converter IC or other cct to process 
its output. These may be boost, buck or buck-boost depending on what 
the optimum battery looks like. ALL converters will be able to be 
small, including inductor and glue components. Some options may be 
more costly than others, but for a one off project any of the 
topologies will be able to be done at a price that is reasonable for 
the convenience they provide.  Best battery maybe , but almost 
certainly won't be, under about 2v minimum for efficiency purposes.

So, choose your optimum battery and THEN we can start on the best 
converter.



        RM 

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