If it came from the base of the tree the wood grain will probably be squirrelly and practically unsplittable. Get a chainsaw or hydraulic woodsplitter, or throw them in a bonfire. Alternatively, use them in a woodworking project or innoculate them with your favorite mushroom spores.

Well they're about 4ft diameter and not really even possible to move. My electric chainsaw would just burn up trying to cut them, and the cost of a hydraulic woodsplitter wouldn't be cost-effective.

Current plan is just to leave them there until either they start drying/rotting enough to split, or I find someone who wants to take them off my hands.

These are also good for those "Swedish logs" where you drill a hole in the top and the side, and then cut grooves with a hand saw in the top and make a fire right on top.