Batteries are only 7$ per cell to replace the 16650 2500mah (keep power or orbtronic use the Sanyo raw cells ur16650zta 4.35v) that’s if they go bad after 100’s of charges. If you want max runtime you need a 4.35v charger and will have to select 4.35v charge voltage manually . The 4.35v will top off the batts but will show a lower voltage on the charger due to the protection circuit added to the cells. You will get a little longer runtime (~2300mah @4.35v vs ~1900mah @4.20v) but batteries will last ~ 2x more charge cycles if charged to the lower 4.20v.
https://lygte-info.dk/review/batteries2012/Sanyo UR16650ZTA 2500mAh (Magenta) UK.html
I use 2 cells with a couple small nickel coated magnets for a top post since the raw cell is a flat top in my mkiii 60mm, and a single cell in my Ir patrol. 2- cells lasts all night in the mkiii without powering it off, I change the single cell in the Patrol about every 2hrs of constant use.
The patrol only needs the extended spacer for 2 cr123a cells to accept a single 16650 cell. The protected cells will still need a nickel coated magnet added to top of battery to tighten the fit if you rifle mount it due to recoil pulse. This is what has been working for me close to a year now with no problems. Charger and 4 batts under $80. It’s the mkiii extended end cap that costs $$$ if you can’t make one. .75mm thread pitch is what I cut and works fine.
The irx package is a turnkey unit for the mkii and mkiii at a good price that will pay for itself vs throwaway batteries if you use it long hours.
For the Ir patrol a charger and 16650’s are all that’s needed if you have the extension for 2 cr123’s.