A battery backup unit module is dimensioned to fit on a height of one rack unit of an electronic rack, and one third of a shelf width of the electronic rack. A cell pack of the battery backup unit module has batteries arranged parallel to the front of the electronic rack. There are 14 groups of battery cells. Each group of battery cells has six battery cells connected in parallel. The 14 groups of battery cells are connected in series. The 14 groups are arranged as two groups in width of the cell pack, one group in height of the cell pack, and seven groups in depth of the cell pack. In each group, the six battery cells are arranged as an upper row three cells deep and a lower row three cells deep.