Well helllo
I have my Arduino/OKL2-T20 mod sitting here next to me. It collects dust now, and never gets used.
There are some issues with Arduino and controlling mods, though, I am not going to detail them here.
It will work fine for non TC control, super simple. Adding things like live reading of resistance, amps, etc add more circuitry and code of course, though it is very viable, as I did it back in I think May of 2014.
I am holding my experiences and undisclosed limitations of the Arduino platform for mod control until the Ares chip is released to the public. I really want to see how Whiteout get around a core issue that, thus far, no one has mentioned anywhere that I have seen, nor is any Arduino currently on the market capable of solving
OH ... and there is a postage stamp sized arduino based device if you are looking for the smallest one available that will suite a mod perfectly. It is TINY! I bought one before finding the rock wall limitation to Arduino that I could not resolve and never did another Arduino mod because of the issue.
Find it here:
http://femto.io/
Concerning batteries:
I used a Lipo because the DC to DC converters that I found suitable for a vape device were all incapable of running efficiently off of a single 18650 and providing good power. Lipo was chosen because i was trying to keep the device small, and 2x18560 + sled + contacts + wire etc added more space requirements than a single 2S2P Lipo did. I really hadn't considered using Ti/SS wire at that time so the ability to do both buck and boost was limiting selection of converters that would work. As a result I just went buck only and started from 7.4 volts so I could still hit high power with a coil made of Kanthal A1.
These days, using a SS coil and a single 18650 would open up the field of selection for DC to DC converters a bit and work just fine.
EDIT: BE WARNED THAT CODE HAS ERRORS IN IT. THE SCHEMATIC ALSO HAS ERRORS IN IT.