Lead-acid batteries are a mainstay of power backup systems in data centers, as well as many other applications where high capacity and rechargeability are required. Although they have been incrementally improved over time, these batteries have several drawbacks: They’re highly corrosive, they have limited economic life, they’re heavy and they require substantial space. Given that lithium batteries are being rapidly developed for electric and hybrid vehicles, they may have applicability for data centers, if their high cost can be substantially reduced. (Lithium batteries are about five times more expensive than lead-acid batteries for the same power capacity.)Lithium batteries’ principal benefits are that they are about one-quarter the weight and take up about one-half the space of lead-acid equivalents. However, if their costs can’t be substantially lowered, they will have limited data center application.