A little update.. I tested the resistance of the connectors and is very low now! After all this tiny pieces of metal maybe were lost in stan junk... But it makes a very big diference... I found that a spring with 6mm long inside the connector plus a 3.8mm diameter 6mm long ss rod for the outer electrode are ideal and 8mm for the inner electrode connectors... I found that it can have a smal angle on the side that contact the spring, because it makes the spring force the rod in the wall of the hole improoving the contact!
The tip could have also an angle ... Basicaly doing it with low precision is a good idea..
Now im confident to push more than 10 amps thru this cells...
I noticed my cell has a wrong desing in the water input position ... Mine is alligned with cell n 4 and it actually made me think...
If we apply voltage in series there is going to be movement of ions...
Im thinking if perhaps there was some sort of secret in this botton part!