I jan 2002, Consumer Reports did an article on these items. They didn't test the Coleman. They rated the Booster Pack J900 as "Excellent" Two batteries are handy if you have intermittent heavy loads, like an electric winch, large compressor, or a welder. They are also handy for campers, where you can run all your lights and stuff off one large deep cycle battery, and save the starting battery for the vehicle. Otherwise, it's a waste of money and adds a lot of weight to the front end. Remember, once the engine is running the battery has no role in the operation of the vehicle. Power will only be drawn from it if the alternator can't keep up with demand.