Lithium Polymer/LiPo set to power Arduinos I want to switch from using disposable 9V blocks to a proper setup of 3.7V LiPolys for all my portable Arduino (Uno/Mega) projects consisting of:


only 3.7V LiPo units
charger
upconverter (to 5V)


My questions:


Is this generally a good idea? Or is there a better solution for portable Arduino power?
How should I actually hook the LiPolys up to the Arduino? They usually ship with JST connectors. Should I use the Vin/GND Pins or should I build my own JST/DC-Connector adaptor? I want to create a robust, pluggable solution.
Am I actually losing power twice that way (once in the upconverter and then in the Arduino voltage regulator)?
If you can get away with it, I recommend not using a boost converter and instead connecting the battery directly to the supply voltage input (the "5V" pin).

The AVR chips used in most Arduinos (but not the Due or Zero [and the Yún and Tre are a totally different kettle of fish entirely]) can operate with anywhere between 2.7 and 5.5 volts, with the ATmega328P found in the Uno able to run with as little as 1.8V. This is a much larger range than the 3.0-4.2V available from rechargeable Li-ion/Li-poly/LiFePO4 cells.

Naturally you will need to make sure that any external components can run with the reduced voltage as well, but quite a few are able to work with anything from 2.0 to 5.5 volts.