Old_NFO made a comment on my build blog about the EOTech 516. I've looked into it and read any info I could find on the model and the batteries it uses. I'm sold. Change my holosight to the 516 from the 512. I've talked with many people around here about NV (night vision) compatibility. I haven't found one yet that has actually used the feature. If there's anyone out there that has actually used the NV feature, please pipe up and let me know.