WARNING: The following article contains spoilers for Justice League: Last Ride #6, on sale now from DC Comics.
Darkseid's recent return in Justice League: Last Ride #6 (by Chip Zdarsky, Miguel Mendonca, Enrica Angiolini, and AndWorld Design) shows him at what is perhaps one of his strongest states ever. Having absorbed the power of the Green Lantern Central Battery, Darkseid now has access to a powerful cosmic force fueled by his insurmountable willpower.
Darkseid's new powers bring up the question of his fascination with the emotional spectrum, a power he has history with in the mainstream DC Universe as well as the DCEU.
Darkseid is best known for his ongoing conflicts with the New Gods of New Genesis and the Justice League, most specifically Superman. But as the universe's most well-known tyrant, Darkseid has enemies among the more moral forces of the cosmos, which includes the Green Lantern Corps. In Green Lantern 80-Page Giant #3 (by Scott Beatty) The Guardians of the Universe, concerned by Darkseid's schemes, assigned a Lantern, Raker Qarrigat, to patrol the sector occupied by Apokolips and keep tabs on its ruler. Unfortunately, Darkseid defeated him, and that victory gave Darkseid time to study the broken ring he shattered, perhaps first sparking his interest in the power of emotion.
Since then, the Green Lanterns have been part of Darkseid's main opposition. This even extended over into Zack Snyder's Justice League, where the initial coalition to stop Darkseid's conquest of Earth was comprised of Old Gods, Amazons, Atlanteans, Humans, and a Green Lantern. There would have been further exploration of this intergalactic conflict had Zack Snyder gotten his way, but production of the movie could only allow for a brief reference. Regardless, this demonstrates how prominently the Lanterns have opposed Darkseid's bid for conquest.
This brings the focus back to how he took command of the Central Battery's power. He simply seemed to direct its energies into him, siphoning off enough to become fueled by it, perhaps even becoming the new carrier of the Battery's spark. This seems highly unlikely, considering that Darkseid is inherently evil and the Lanterns are considered a force for good. Yet, history has shown that one does not always need to be virtuous to be gifted the power of Lantern. Sinestro was once a Lantern, and there was an alternate version of Bruce Wayne who got a ring and used its power for evil. The simple truth is that willpower is an emotion everyone has, whether they choose to be a hero or villain, and Darkseid has one of the greatest wills in the DC Universe.
This also explains why he was able to overcome Hal Jordan and use his body as a puppet until his plans came to fruition. If Darkseid's will was great enough to steal the power of the Green Lantern Battery, then it stands to reason that he could dominate Hal's mind. It also stands to reason that with the power of the battery at his disposal, Darkseid has become even more powerful than other gods of the emotional spectrum such as Ion and Parallax, making this form one of his strongest to date.