If you have a laptop or other device that will connect with an USB->RS232 cable, and using the Morningstar TS-45/60 interface and software, you can get real time monitoring of the solar system. After you get the charge setpoints configured in the software and fool around a few days noting the harvest at all times of day, a stand-alone monitor is less a "must have". These remote monitors are good for assessing daily use and harvest total, along with voltage measurement. The battery temp sense wire IS a "must have". That's what makes the total system an excellent charger.