Pros: saves on weight, has a longer lifespan (per charge and overall), generally carries a better warranty than lead from what I have seen, and all the "cool" kids have them
cons: costs are significantly higher, battery power is "all or nothing" they don't get weak they just die, not all onboard chargers are compatible with maintaining the duty cycle of a lithium cell, I have also heard of lithium batteries affecting graph performance (I have no evidence just rumors). AND last but not least lithium/cobalt mining and processing is a very water intensive process that produces ALOT of contaminants, there is research going on now around the adverse affects that lithium battery manufacturing has on local water supplies.... I am not by any means a tree hugger, but as an angler I have a hard time supporting a product that may eventually cause long term issues on a pond near me... just my $.02