Hello, as has been said the batteries are in parallel so it's just the voltage of one cell.
the easiest way for electronics newbies (that includes me as we are all always learning) :jester: to do it would be the use of a regulator,
This is a 3 pin device , one pin is connected to supply ground, one to supply positive and like magic the desired voltage comes out the other pin.
hear is a link to a texas instruments one it cost about 35 pennies.
http://uk.rs-online.com/web/p/linear-voltage-regulators/6616737/
i have linked to one that is rated at 0.5 amps , this would be with a heat sink, without one it will do about 1/3 of that.
it will output 3.3 volts with any dc voltage applied up to a maximum of 25 volts, so any cheep dc supply could be used, it will get hotter with a higher input voltage as it is just wasting some as heat to drop the voltage so closer is better i.e. 5-12 volts seems ok.
Also as someone else mentioned I would recommend soldering direct to the contact pads, you may need to use an abrasive to take the coating off of them as the solder may not adhere to the coating.
also carefull about the solder , newer electronics are lead free and so all fluxes and coatings used dont like lead solder much (experimentation is the only way to find out I find) although if you remove or scratch the coating either should work ok.
One regulator should be ok to run 3 or more as I would think they are very low current draw (a few milli amps) i have a real cheep digi vernier that Is very flaky so i will try to pull that apart and measure current draw.
Hope that all makes sense.
If you need a more detailed description let me know and i will try to do a neat drawing.
Stuart