A battery pack for use in a device comprising a plurality of lithium secondary cells connected in series, in parallel, or in a combination thereof, wherein each cell comprises: a positive electrode including a lithium transition metal phosphate compound wherein the lithium transition metal phosphate compound has a specific surface area of greater than 15 m 2 /g; a negative electrode including a carbon-containing lithium intercalation compound wherein the carbon-containing lithium intercalation compound has a particle size less than 25μm; an electrolyte in contact with and separating the positive electrode and negative electrode wherein the electrolyte includes 0.8 M to 1.5 M LiPF6 and an organic solvent including 30 wt% to 70 wt% ethylene carbonate, 0 wt% to 20 wt% propylene carbonate, 0 wt% to 60 wt% dimethyl carbonate, 0 wt% to 60 wt% ethyl methyl carbonate, 0 wt% to 60 wt% diethyl carbonate, and 0 wt% to 5 wt% vinylene carbonate, wherein the sum of the weight percentages of ethylene carbonate and propylene carbonate is between 30 wt% and 70 wt% of the total organic solvent, and propylene carbonate represents 30 wt% or less of the sum; a positive electrode current collector in electronic communication with the positive electrode; and a negative electrode current collector in electronic communication with the negative electrode, wherein the cell has an operating voltage of less than 4.2 V, the components of the cell are selected to provide an area specific impedance of the positive electrode at least 3 times of the area specific impedance of the negative electrode, and a total area specific impedance of the cell less than 20 Ω-cm 2; and wherein the cell exhibits impedance growth of no more than 10% for every 1000 deep discharge charge-discharge cycles at a temperature of up to 60°C, and wherein the deep discharge in the charge-discharge cycles is at least 50%, and the cell is charged at a rate greater than 1C; wherein the pack has an initial available power that is no more than 20% greater than a predefined power at end of life, and wherein end of life is the point at which the pack has undergone at least 300,000 deep discharge cycles. a positive electrode including a lithium transition metal phosphate compound wherein the lithium transition metal phosphate compound has a specific surface area of greater than 15 m 2 /g; a negative electrode including a carbon-containing lithium intercalation compound wherein the carbon-containing lithium intercalation compound has a particle size less than 25μm; an electrolyte in contact with and separating the positive electrode and negative electrode wherein the electrolyte includes 0.8 M to 1.5 M LiPF6 and an organic solvent including 30 wt% to 70 wt% ethylene carbonate, 0 wt% to 20 wt% propylene carbonate, 0 wt% to 60 wt% dimethyl carbonate, 0 wt% to 60 wt% ethyl methyl carbonate, 0 wt% to 60 wt% diethyl carbonate, and 0 wt% to 5 wt% vinylene carbonate, wherein the sum of the weight percentages of ethylene carbonate and propylene carbonate is between 30 wt% and 70 wt% of the total organic solvent, and propylene carbonate represents 30 wt% or less of the sum; a positive electrode current collector in electronic communication with the positive electrode; and a negative electrode current collector in electronic communication with the negative electrode, wherein the cell has an operating voltage of less than 4.2 V, the components of the cell are selected to provide an area specific impedance of the positive electrode at least 3 times of the area specific impedance of the negative electrode, and a total area specific impedance of the cell less than 20 Ω-cm 2; and wherein the cell exhibits impedance growth of no more than 10% for every 1000 deep discharge charge-discharge cycles at a temperature of up to 60°C, and wherein the deep discharge in the charge-discharge cycles is at least 50%, and the cell is charged at a rate greater than 1C; wherein the pack has an initial available power that is no more than 20% greater than a predefined power at end of life, and wherein end of life is the point at which the pack has undergone at least 300,000 deep discharge cycles.