I spent quite a few January nights pig hunting and had to replace the AA batteries in my DigiSight EVERY night so I needed an external battery pack.
I did manage to take down 9 pigs that basically had a hall pass during regular deer season!
I have a bunch of different torches and IR illuminators that take 18650 batteries and have chargers for them so that made battery choice easy.

I ordered some battery holders and right angle plugs and made my own external power supply that fits into a small digital camera case that it ziptie to my weapon.
I'm sure it's been done before but this is my version that's dirt simple and easy to do.
Popping the batteries out and charging them in pairs is not a problem.
For this project, I chose these particular right angle plugs because they are modular and very easy to solder so anybody could do it.

This works with my Photon and my Pulsar N750A and will work with a bunch of different NV scopes but check your particular requirements.
Disclaimer: I'm not responsible if you do something wrong and become all blowed up - once the magic smoke escapes from your electronics, you may never get it back in there so only proceed if you are confident of your abilities.

Parts List (mostly scrounged off of ebay with free shipping)
If you buy everything new, it will run about 35.00 total and you will have 9 extra connectors and 3 battery holders.
18650 battery charger - 6.50
6 ea 18650 batteries - .99 to 4.00 each - these are cheapies that run about a 1.00 each but run NV for many hours
Right angle 2.1x5.5MM DC power plug - 10 for 5.45
2 ea 3X 18650 battery holder - 5 for 5.49
2' 1/8" ID heat shrink tubing - had this laying around but should be 2-3 bux.
1" of 1/2" heat shrink tubing - had this laying around but should be less than a buck.
2' of 18 gage wire in red/black or whatever color you have around - this length lets you put pack on stock or foregrip but it's your custom so make it what you want.
1 small digital camera case - just had this one laying around, pardon the dust - around 5.00.

Finished product:


Parts pile next to finished product:


18650 Batteries and charger:


18650 battery holders - wire two red wires together and run to positive terminal on plug and wire two black wires together and run to negative terminal on plug:


Modular plugs that are easy to solder - positive to tab on top, negative to tab on right:


Assembled and ready to slide into camera case:


Place battery holders back to back and slide into case.


There you go, hope it saves you some bux on batteries!

Thanks.
Tag for later.....

I forgot to include the wiring diagram in the first post.
I can't edit the first post so here is the diagram.
Sorry 'bout that....and hope that helps!

Or you could just buy these I use. NCR18650 battery pack

I gotta admit, those are pretty cute!
I looked at those and was considering doing the same thing with 2 cells in series instead of 3.

The only problem is most NV scopes require 8-15 volts.
18650 batteries are nominally rated at 3.7 volts.
Fresh 18650 batteries fully charged put out approximately 4.2 volts.
2 fully charged batteries would be about 8.4 volts.
2 of them at nominal charge would be 7.4 volts - under the required threshold for most NV.
If it's not fully charged, it may or may not turn on the NV.
If you use better batteries you should be OK for light use.

This pack started out at 12.3 volts and after more than 4 hours use with IR on my Pulsar N750A, it was still at 11.7 volts with cheap 18650 batteries.