I have used the rechargeable CR123s that DirtyTough mentioned and they worked OK for me as well. For those mentioning Bering doesn't recommend rechargeable 123s, the answer is they do not recommend rechargeable CR123s in thermal or night vision devices. Yes, the Hogsters are rated to handle the 3.7V power provided by most rechargeable 123 batteries. However, it is a concern of over-charging batteries, batteries providing inconsistent voltage, plus adding recoil to the mixture.
I have used rechargeable 123s on a R35 when used as a scanner. However, I would highly recommend using a voltage meter and making sure the rechargeable batteries you are using are not providing a higher voltage than expected (3.7V). When using it as a rifle scope, I would recommend a 5v battery pack. I personally like the Anker style batteries. They are tested to extreme low temps. Many other brands seem to have difficulties in colder weather.