Good idea to use the galvanised screws as it should give you more surface area
I actually hadn't considered that but I did observe how these small screws produce a similar output to the much longer bolts which have a flat surface. This must be why! Thanks for clearing that up in my head.
Am a bit new to the electrical side of life so I don't know clearly what you mean when you say "Did you try testing with a load in series". Are these cells not already in series?
It is possible I am not understanding how to read my multimeter?
I see a small m on the meter when I am reading Amps, but struggle to believe this is producing just one 1000th of an amp.
I checked the resistance in those two cables (black and red) and they seem good, giving me a strong reading, so I don't think it relates to damaged wires.
Sorry for the delayed response. I believe you need to check the amps like in this image. Where you let the electricity flow through the bulb and through the multimeter. This way you will get a better idea of how many amps the bulb draws and how much the batteries can give.
I am still learning myself but really find all this fascinating.