The answer is simple. Lithium is a better product than AGM. Lithium is lighter, more compact, and powerful, it will also last longer. However, a lithium battery will cost more, because it is a highly sought after product. Almost everything that has a battery nowadays will have a lithium battery. Mobile phone, Electric Car, Electric Bike and Skateboard just to name a few. There are situations where you can get away with an AGM battery. If you only need about 100ah (most 4 x 4 setups), you can purchase 1 x 100ah battery and a battery box and away you go. However, once you start getting into the larger amperages (200+) it really makes more sense to turn to lithium.