Detach old battery pack (photo 1) from circuit board. My power leads were crimped, and easily de-crimped with a needle nose pliers.

Gently pry 3-wire female plug from circuit board.

Disassemble/desolder old pack. Loose assemble the new batteries. I used the old holding bracket (photo 2) and wires.

Solder batteries together according to schematic (photo 3.) Wrap completed pack in shrink wrap or electrical tape.

Connect (+) and (-) leads with crimps, solder, or small wire nuts. I used wire nuts.

Reconnect 3-wire plug to circuit board.

Place battery pack in handle location, and reassemble vacuum.