There are several ways to do it, depending on how much you want to spend, how much storage capacity you need and how much rigging you want to do.

Here are a few options:

AC power pack - $130

On remote shoots, I use the dummy battery and a portable AC source like this 24aH power pack (with built-in AC inverter). I've done it this way since GH2 days and it works.

Wooden Camera V mount plate with GH3/GH4/GH5 dummy battery included - $250 (plus the cost of the V mount battery)

Amazon charges for shipping and B&H is out of stock. You can get it with free shipping from Adorama. A 10.4aH V-mount battery and charger will cost you an additional $209.

Panasonic GH5 Battery Grip - $347.99

The other plug and play possibility is the GH5 battery grip. Sadly, this is a pretty expensive solution and only adds 3.7aH to your storage capacity.

Hope this is helpful and good luck finding the external power solution that best meets your needs!