High performance battery packs are described especially for use in electric vehicles and plug-in hybrid electric vehicles. Based on high energy lithium ion battery designs, the battery packs can have pairs of parallel connected batteries to supply an energy capacity at full discharge of at least about 40 kilowatt-hours or in alternative embodiments a set of all series connected batteries that can produce at full discharge at least about 15 kilowatt-hours. In some embodiments, lithium rich positive electrode active materials can be used to faun the batteries in which the material comprises a composition approximately represented by a formula xLi2M′O3.(1−x)LiMO2 with x from about 0.05 to about 0.8.