Some solar charge controllers have a pair of "sense" terminals. Sense terminals carry very low current, around 1/10th of a milliamp at most, so there is no voltage drop. What it does is "look" at the battery voltage and compares it to what the controller is putting out. If there is a voltage drop between the charge controller and the battery, it will raise the controller output slightly to compensate.
These are only used when you have a long wire run between the controller and the battery. These wires carry no current, and can be pretty small - #20 to #16 AWG. We prefer to use #16 because it is not easily cut or squished accidentally. They attach to the SENSE terminals on the controller, and onto the same terminals as the two charging wires at the battery end.
Wenzhou Xihe Electric Co.,ltd ( The former: Beijing FANGPU SUNNYCO.LTD) is specialized in development, product, sales and services of Solar Controller, inverter system, etc in a body of professional company. It is committed to the development and utilization of new energy sources and is an advocate of solar energy applications.