That is the battery clip adapter(was) dual lock, charger, LiHV batteries I use
I had the top battery clip adapter on my last drone, had good results,I had plenty of 18-19 odd mile round trips. This year I’ve gone direct mod that should give me a little bit more due to a much better amp/volt flow than just the slits touching the terminals on the top mounted one. I glued mine on as removing it a few times wears the slits and becomes a little lose. I also modified mine to sit upright so the battery can sit forward without covering the gps at the back.
You can buy it cheaper from here http://www.uavmods.co.uk/store/products/47495-dji-mavic-pro-power-platinum-adaptor-dual-xt60
They have made the copper strips a little longer so it sits more towards the front to be easier to plug a top mounted battery in without the battery sitting over the gps at the back, BUT I’m not sure it’s far enough as I’ve never tried their battery clip. If you mount the batteries on the side with a top clip, from my experience it would be a pain keeping the wires away from the props.
Here’s my modded clip and setup from last year