The GS-21 and GS-52 are 9 volt alkaline battery packs. New brand name cells are first tab-welded together and then entirely encapsulated in non-hazardous epoxy. The potting material is added through a portion-controlled pouring process and totally covers the bottom, top, sides, and spaces between the individual cells, virtually eliminating failure-causing air bubbles. All batteries must meet our rigid quality control standards. They are hand inspected for air bubbles in the poured potting material. Finished batteries must pass through a size gauge measuring width, height and depth. They are further tested for proper voltage and visually inspected by the QC department.