The two large red batteries are old NEDA 1603 9V batteries that originally came out of the Motorola transistor radio in the back (model T18B, manufactured in 1960). Those two large batteries, operated in parallel, have been replaced by a "normal" 9V battery like the Duracell, which I showed for size comparison. The + and - terminal design was the same, they are just much larger in the old 9V's. I am not sure where the 8.4V Mercury battery came from, but you don't see those very often either. The Motorola still works great and runs a long time on just a single 9V.