Battery options

For my SensorStick I need at least 3 volts since the DHT11 only works from 3v0, all of the other sensors can work with lower voltage. A single coin cell will not be suffice since the voltage curve of such a cell decreases a little on the longer run.

This is my target for the sensor stick:

• Runs at 3.3 volts using low quiescent regulator
• Uses an average current of 50uA
• Should run on battery for at least a year

At 50uA power usage and running for a year we need a battery that has: 50uAh*24hours*365years= 438mAh. So at least 438mAh is needed. Please note the battery internal drain, so we need more than calculated.

So here are my options

• 4x coin cell CR2032
• 6v 
• 440mAh
• Small size, but consumes lot of space on PCB since it must be directly/flat attached to pcb
• 2x Double coin cell holders will cost 1.80euro @Digikey, BH800S
• Boost converter
• single cell from 1.5v would work (AAA)
• increased component/PCB cost, around 3 euro 
• increased sleep current
• increased noise for the capacitance measurements
• Not an option due price tag.
• 3x AAA batteries
• 4.5volts 
• 700mAh
• Alkaline cells has higher voltage drop in voltage curve than coin cells
• PCB mounts cost total 1.30 euro (BK-82 @digikey)
• Seperate AAA holder box cost around 50 eurocent @ebay
• 9v block
• 9volts
• 900mAh
• Higher voltage drop, just like AAA. But since it is 9 volts battery, we have a high margin.
• Consumes a lot of space.
• Battery snap-on wire cost 20 cent @ digikey
• Battery holder 60cents @ ebay or 1 euro @digikey

Putting all the things together, I currently think it is best to use the 9 volt block with snap-on wire.