Reddit reviews HEDBOX | Unix-BM | V Mount V-Lock Adapter Plate, for BMPCC 4K and 6K, with 1x USB 5V/2.1A and 3X D-Tap 14.8V/148W Power Out, Regulated 12V/50W Power via 20in/50cm Breakaway Cable 2-Pin Connector

I love this v-mount battery plate:

HEDBOX | Unix-BM | V Mount/Lock Battery Adapter Plate, with 1x USB 5V/2.1A and 3X D-Tap 14.8V/148W Power Out, Regulated 12V/50W Power via 20in/50cm Breakaway Cable with 2-Pin Connector for BMPCC 4K https://www.amazon.com/dp/B07K1M23QN/ref=cm_sw_r_cp_apa_i_C5tADbDQHV0EM

It has 3 D-Taps and one USB port (powering a small monitor) and it comes with the 2-Pin connector cable that plugs right into the BMPCC4K!

You will need to mount it onto a plate on your rig. I got this camvate and it mounts perfectly but there are others.

CAMVATE Multi-Purpose Mounting Cheese Plate https://www.amazon.com/dp/B071YTFZ88/ref=cm_sw_r_cp_apa_i_99tADbVK192QQ

Finally if you want to save a little money on vmount batteries you can use this alternative until you save up for a good v-mount:

This $20 v-mount adapter attaches the Hedbox to give you the option to use NPF batteries.

Neewer NP-F Battery to V-Mount Battery Converter Adapter for LED Light, Field Monitor, 5D2 Rigs, Alternative Battery Option for Sony V-Mount Gear, Fits for 2-Pack Sony NP-F970, NP-F770,NP-F570 Battery https://www.amazon.com/dp/B075R8DMKF/ref=cm_sw_r_cp_apa_i_m6tADbQCDAHW2

And you can buy 2 NPF 970s for $35

NP F975, NP F970, NP F960, NP F950 2X Replacement Li-ion for Sony DCM-M1 MVC-CD1000 HDR-FX1 DCR-VX2100E DSR-PD190P NEX-FS700RH HXR-NX3 (Dual Battery) https://www.amazon.com/dp/B01J7S0VNQ/ref=cm_sw_r_cp_apa_i_F.tADbW4H2N5V

Cheap $16 NPF dual charger:

Powerextra Dual Battery Charger with USB LCD Display for Sony NP-F970 NP-F930 NP-F950 NP-F960 Battery https://www.amazon.com/dp/B07G7MJKRP/ref=cm_sw_r_cp_apa_i_yguADbDG636AC

$27 dual charger with LED:

SR SUN ROOM NEW Dual Channel LCD Display Charger For Sony NP-F550 NP-F570 NP-F750 NP-F770 NP-F930 NP-F950 NP-F960 NP-F970 NP-FM55H NP-FM500H NP-QM71 NP-QM91 NP-QM71D NP-QM91D Camcorder Batteries https://www.amazon.com/dp/B01CG7P4YQ/ref=cm_sw_r_cp_apa_i_EfuADbN81BWDN

I run this setup and it works GREAT!

So, its not as cheap as a v-mount plate. But I'd suggest getting a HEDbox V-Mount adapter for the BMPCC4K. Its a fantastic plate, and I use it currently. It has a direct power connection to the Camera itself, which allows you to keep a Battery in the camera, in case there is any sort of drop out. Not overly expensive, and a good product. It has 3 d-tap ports, and a USB port along with the power cable, so it has a lot of options to use other peripherals.

HEDBox Unix BM - $125 + 15 s&h.

SmallRig Battery Plate- $36-ish

SmallRig 15mm Mounts - $15

And of course your V-Mount Battery of Choice.

Hopefully this helps!

I actually had an old v-plate that I had lying around and repurposed for the rig. The SmallRig v-plate should work fine, but it's a dead plate. Has no d-tap of it's own, so would need batteries with dual d-taps or a splitter.

This one I've also heard is good, but can't vouch for it first hand. Wouldn't need the cable I provided earlier either as it's built in. Do something with dedicated d-taps to make switching batteries easier (no unplugging cables form battery)
https://www.amazon.com/dp/B07K1M23QN/ref=cm_sw_r_sms_apa_i_V3NMDb2FYEKRQ

This is the shoulder wedge I have it attached to (both are vertical) in order to press into the front of my shoulder for controlled movement.
https://www.amazon.com/dp/B00N4OZUPO/ref=cm_sw_r_sms_apa_i_q6NMDbRY0D66N