Gonine DMW-DCC12 AC Power Adapter DMW-AC8 Plus DC Coupler Kit (PANASONIC BLF-19 Battery Replacement) for PANASONIC DMC-GH3 DMC-GH4 DMC-GH3K DMC-GH4K D https://www.amazon.com/dp/B01EI2S6OC/ref=cm_sw_r_other_apap_lRXTOpUnqiXSv
I think this may be the same as what u/RedditFandango posted, but I have been very pleasantly surprised by how well this works!
https://www.amazon.com/dp/B01EI2S6OC?ref=ppx_pop_mob_ap_share
I've been using the Gonine one for the past 6 months and it seems to work fine.