204,
In case you are not aware of this, any use of rechargeable, internal batteries in a Hogster, Vibe, or Yoter using CR123 or 16650 batteries are use at your own risk per Bering Optics. Bering will cover normal warranty items but if the batteries leak, catch on fire, explode etc, the damage caused by them will not be covered.
As for using them, I tested the one called the OEM one and the 3D Night Vision. I didn't try the Apex 3D one. The pros of both the 3D night vision and Apex 3d is they can utilize a larger variety of 16650 batteries.
For the OEM version, many of the protected 16650s are too long. I have used both Jesspower and Taken brand batteries with the OEM version, and they fit for me.
I believe all 3 of them have a place to put the existing cap so that is not unique to the 3D Apex version. The OEM version is the most expensive, but it also seems to be the smallest, and fits the nicest. I tried the 3D Night Vision one after I saw a video of him literally smacking with full force a number of times and the unit didn't shut off.
Night Goggles has chosen not to sell any of the three 16650 extenders as we do not feel right selling an accessory that we know is not covered by warranty. It frustrates me that there are dealers, manufacturers, and suppliers continuing to sell these without telling their customers the risk. I know there are lots of people using them, and they will be fine until something happens. Just know the risk. Before I would buy one, I would ask the company you buy it from if they will cover any thermal damage if something happens because of the rechargeable batteries. If they say yes in writing, then I wouldn't worry a lot about it. If they say Bering will cover it, this is not what Bering has told me, and I have asked numerous times.