Lithium batteries are much lighter and have a higher power density than lead acid or nickel cadmium cells. They also have better discharge characteristics because they maintain a constant voltage until depleted. With lead acid batteries the voltage slowly decreases over time which can also decrease the read range.
Lithium polymer batteries cost more than the same sized lead acid size but have 1/6th the weight.
Lithium batteries require chargers designed for them. Chargers for lead acid batteries should not be used.