> instead of powering the devices with 12V and letting the linear

Yes, I would certainly look at DC-DC conversion rather than
waste power through linear regulators

You should be able to get > 90% efficiency

I've tried some of the 1-2-3 cell boost converters, from Microchip
and others, and found them very good

This one, MCP16301

http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=3Den554058

looks a likely candidate, even if it means using a couple in parallel

Input 4-30V, output 5V @ 600mA, up to 98% typical efficiency

Joe
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