For the Reap V1 there are a few options. The IRX, UNV Anker, and TNVC TRB being the most popular and I have all 3.
The IRX uses rechargeable batteries so there is no cable. But mine only gets between two and a half and two hours forty five minutes per set. Hot or cold, bright or dim, heavy or light NUC....does not matter. This causes some anxiety for me as I have to keep time and know when to swap batteries and hope it is not about the time the piggies come out. I have forgotten.
The UNV Anker kit has a cord from the battery compartment to the Anker which is mounted via a pouch on the stock. Works great and I use it currently on my Hunter 60 although it can be used on the Reap V1. Cost is an issue at over $300. I probably would not have paid that for it but got a deal for $100 off a FB hunting group.
Best value I think is the TNVC TRB. I do not like the forward rail mount either, however there are a couple good hacks you can do to mount otherwise.
One, buy a Anker 5000 mah round battery and add Velcro to the bottom and/or top of the Reap battery compartment . Attach the battery then use a 12” Velcro strap to cinch it on tight. See picture below, the TRB cable is just long enough to wrap around the scope housing and plug in. Works great and I have not had any issues with scope or battery function nor comfort with setup when carrying with a sling.
Second option, buy a 3” USB extension off Amazon and mount the Anker battery included with the TRB on the stock. Ditto on the Velcro for the stock and battery then use the 12” Velcro strap to cinch it tight. Also use a Velcro strap to keep the cord tight to the buffer tube, just make sure the buckle is positioned where the charging handle does not catch it. This option works well and the battery is out of the way and counterbalances the rifle. One of my hunting buddies runs this exclusively on his Hunter 35 no issues. Hope this helps.