And no I cannot quite explain it, maybe they use a slightly different formula, I have no idea 
"And no I cannot quite explain it, maybe they use a slightly different formula, I have no idea "
Well there are variables, ambient temperature, not measuring voltage under an actual current load, calibration factor of meter, etc. But they are not considered 1.5 volt cells by any means 
Lefty
1.5 volts you read right after a charge is a no-load surface charge voltage, doesn't mean anything. The nimh (and ALL batteries) quickly drop down to their rated voltage when asked to do any work. No interesting magic here, sorry.
Yes and some devices don't like that
Actually 1.5 volts could mean something, Your charger might be broken
"Fresh" batteries run slightly over the rated voltage, especially with low loads (like an arduino.) NiMH/NiCd (1.2V nominal) can be up around 1.5V, Li-ion and Lipoly WILL be 4.2V, Alkalines can be up near 1.7V, and lithium (non-rechargables "1.5V" AAs aimed at cameras and such) as high as 1.9V.
All of which is a bit annoying if you were planning on connecting 3xAA cells directly to your arduino; the voltage can be higher than safe.
The Arduino AA undershield that people are mentioning actually includes a boost regulator, so it'll happily take any two AA-like batteries (1.2 to 1.9V) and spit out 5V regulated for the Arduino.
You can also use something like Adafruit's "Minty-boost", which gives you 5V from 2AA, on a USB jack...
I've got a question. I've been using Arduino for a while now but never really got into anything other than USB power to my Arduino Duemilanove. A friend of mine recently gave me an Arduino Pro Mini, 5V 16MHz. and my main issue now is that I can't power, and get my code to run, it without it being on a USB.
I am giving it 9v from a battery over the RAW and BLK pins, the LEDs are lighting up but it doesn't seem to be running my code.
I was wondering if anyone out there might know how I am messing this up. Thank you in advance and sorry I am still quite new to all of this.