most battery lugs for crimping are a little big for 6awg copper wire. Can I cut an inch off the wire and stuff it in
the lug to fill in the slack before I crimp. All the wires would be crimped together so the contact would be good eh??
no????
Not unless you can generate a huge amount of force. I crunch the lug around the wire with slip joint pliers and then sweat the whole thing with a propane torch & solder. Fries a bit of insulation, but makes a good joint mechanically & electrically.
It is also necessary to use a proper crimping tool - a pair of pliers or a cheap punched steel tool from a motor accessory or discount shop is not really capable of making a good connection. You need a tool that has proper flat dies as part of the jaw where one part of the die crimps the metal part and the other crimps the insulation to provide strain relief in the case of insulated crimps. Even for uninsulated crimps a decent tool is required - not cost effective if you don't use it regularly.
If you don't have a decent crimping tool it is best to solder.
However if you do possess a quality tool and really can't find the correct size connector I don't see any technical problem with filling up the excess space with copper strands since the pressure exerted by the tool should compress the whole thing into a homogenous mass.
A bit of a rant perhaps but I work in the power distribution industry where quality connections are essential and the correct tooling worth its cost - in fact we go as far as only using tooling from the same manufacturer as the crimp connector to ensure consistent quality. When we recently changed manufacturer all old tools had to be binned even though some were only weeks old!