Run with what you have for now. If the plan is to charge faster, you need to either parallel with another wire (larger if possible), or possible use the existing wire to pull a new one.
I would start by putting a digital volt meter from the positive of the charger output to the battery positive, measure the voltage. Repeat on the ground / negative side. add the two together, and that is your voltage drop - the higher the amperage the higher the drop - test when you are running max amps (bulk charging) to get a worst case.