RE: what is-A123 battery?
A123 Systems is a company. The batteries they make of which we use are a Lithium Ion type. If I remember corectly, I think the chemisty is LiFePO4, just google that for more info. As for longer and safer, depends upon what you are comparing too. A 1000Mah battery is 1000Mah reguardless of chemistry, but A123 have a pretty high energy density so they are fairly light for thier capacity, but not as light as a Li-poly. The A123 chemistry is safer than other Li-Ion types, but still probably not as safe as say a Ni-Cd. The main advantage of A123s in my opinion is not longer or safer as the OP put it, but instead the ability to withstand very rapid charges and heavy discharges without an overly large weight penalty.