Yup, any NPF battery 'sled' will work. The metal Smallrig one is great. One caution: Many sleds have multiple power points for 7.4V, say 12v and sometimes 5V. They usually have different size connectors, but just ensure any port with > 7.4V port can ever be accidentally used. Any 5V port can come in handy for charging an iphone or ipad if not in use on the camera when on location.
Just open the dead battery case, remove ONLY the battery by clipping the two leads as close to the battery as possible (leaving as much wire as possible). If need be, solder and shrink-wrap two small wire extensions. Wire a socket to the battery leads (+ to +, etc), drill a hole in the bottom of the casing, install the socket, test the grip contacts with a cheap multimeter to ensure all working, then close the case with a good 'superglue' or plastic epoxy.
Anyone comfortable with a a soldering gun could do the wiring part in 15 min flat.
There are all sorts of variations on how you could do it, but the basic concept is the same - you replace the internal battery with a convenient external source of the right voltage that can deliver the current the camera will 'demand'. The Sony-style batteries work great because they meet the specs, they're cheap, plentiful and come in a wide variety of capacities.