This paper studied a cell selection method and its validation process for the aerospace battery. A cell selection method includes visual inspection, mass and dimension check, electrical tests (OCV, CCV, AC Impedance), capacity measurement and soft-short test. The 6-sigma concept was adopted on data analysis of the cell selection. All the cells outside of the 3-sigma level were rejected, and accepted cells were selected for the validation testing. The validation process executes cycle testing of the four types of 4S string battery group according to the mission operating conditions of the Human-spaceflight followed by analysis of the battery capacity during the cycle and by analysis of non-destructive and DPA (destructive physical analysis) of the cells. The effectiveness of each item on the cell selection method was identified and discussed by non-destructive and DPA analysis with some electron microscope analysis. This paper recommends this proven selection method and validation process for the future aerospace battery.