you MUST charge each cell INDIVIDUALLY to equalizing charges of each and every other cell of the battery pack you are rebuilding.

this is a VERY VITAL AND IMPORTANT STEP that most people often forget. your battery is only as strong as your weakest cell.

you could have a 6-cell battery, and 5 of those 6 cells are 80% charge, but 1 of the 6 cells is only a 20% charge.

your battery is only as good as your 20% charged cell. the 80% batteries will charge to 100% allowing only the 20% charged battery to charge 40% and thats it. it wont charge no more.