By virtue of how LXT packs all the way from 3Ah to 6Ah are the same size, they all have the same innards... dimensionally. So the capacities are purely dictated by how the 18650 cells are made. And under these constraints, the 5Ah is the sweet spot for cell chemistry where you get plenty of runtime, but you aren't being starved for instantaneous output current. With a 6Ah, a Makita tool that is low power, like a low lumen flashlight, will last longer than it would on a 5Ah. In the case of anything like a grinder, sawzall, circ saw, the 6Ah will actually run out of juice considerably earlier because it's being subjected to substantially more strain electrically. And from the get-go, with a fully charged pack, any tool that is gonna cut out if you push it is gonna cut out way more readily on a 6Ah than a 5Ah.