Here's the battery substitute I mentioned earlier. It's not particularly cheap but you won't soon run out of battery with this setup. The inline plug lets you swap out any battery with any camera. The urls lead to the parts you'll want. I have a dummy battery harness for my a7riii, a6500, RX-10 and RX-100, as well as a couple of Canon bodies and six batteries which fit nicely in a front pocket or a belt pouch which I don't use. If on a tripod I use a small bungee to secure the battery to a leg. You will need to cut the usb plug off the cord and splice on one of the white "tamiya" plugs so you can hook to the battery and then to the charger. I show 5000mAh batteries in the pic but lead you to 3000mAh batteries. If you want 5000mAh batteries you can search for them. I have 4 3000s and 2 5000s. 3000 is more than adequate for a day or two worth of shooting. You do need the 8.4v batteries.