Roughly half or more. One 36V 60Ah Sport Series battery (3660-BT) weighs 41.23 lb and replaces three Group 27 lead-acid batteries. Millertech says that cuts more than 50% of the weight. For 12V, a Millertech 100Ah AGM weighs 70 lb, while the 12V 100Ah Dual Purpose lithium weighs 31 lb.