The battery tabs or spot welded to the batteries.

They are in series, meaning they connect from the positive post of one battery to the negative of the next.

Here are the 5 replacement batteries. They are 4/5sub C batteries. This means the are 80% the size of a C battery. 1.3" (33.4mm) in length by 0.9" (23mm) in diameter. 5x1.2V in series gives 6V x 2000mah