The gauge only shows battery voltage and it drops rapidly when you throw a load on the plow pump. The battery is only a storage tank for the alternator output. As long as it jumps right back up when you take the load off you're in good shape. Try turnign on all the stuff you will be running when plowing, then run the plow over against the stops and hold it there for a couple seconds. Watch for how long it takes to bring the voltage back up to 13 volts+. It should come back up in a few seconds. I figure everything is cool if the voltage is up by the time it would take me to back up 100 ft and start another pass.