Found this

https://www.ifixit.com/Guide/Nixon+Watch+Battery+Replacement/44278

http://www.amazon.com/Duracell-D377B2PK08-Watch-Calculator-Battery/dp/B0040E30Z4/ref=sr_1_12?ie=UTF8&qid=1436821235&sr=8-12&keywords=sr66+watch+battery&tag=ifixitam-20

The Nixon Newton has two batteries, one to power the movement and the other to power the backlight. One Sony SR626SW was found in my Newton to be powering the movement and one Maxell CR2016 was found to be powering the backlight.

http://www.amazon.com/Maxell-SR626SW-Silver-Oxide-Battery/dp/B002S49V24/

http://www.amazon.com/gp/product/B000RB00CK/