Yeah they had nicad or nimh batteries donated together to create the battery pack. I had an old shaver that was the same way. Laptops with replaceable batteries do the same things
Current power tools still do this, but with 18650 lithium cells, or some larger variant. But now the trendy thing in power tool batteries are the pouch cells, like the kind found in cell phones and slim laptops. I gotta they’re more energy dense, since there’s less of an air gap between cells.