I'm really happy with my setup, and I use the following :

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https://www.amazon.com/gp/product/B07MW8SQ2G/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I attach my V Mount battery to this and it works perfectly.

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the battery I use is :

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https://www.amazon.com/gp/product/B07JFDZTXL/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

It has two d tap outs which lets me power the camera and the monitor and also has a DC out which I use to power follow focus if I need to.

it's a really simple setup and I'm happy with it.