Little nitpick: Graphene OS isn’t artificially restricted to Google phones. Pixel phones just happen to be the only ones that fulfill the safety requiremets that Graphene OS wants.

Other manufacturers could do the same and Graphene OS devs would welcome it, they just choose not to do that.

I once accidentaly shorted the connector cables of a battery pack with 4 AA batteries. It very quickly generated enough heat to set the insulation of the cable on fire.

Don’t underestimate short circuits!