The electrical charge being provided by the Nissan alternator will supply power to the engine as well as all the accessories in your vehicle. The production of this electrical component should be 13 volts or more. The alternator can be tested in several ways by an owner. A simple hooking up of a voltage meter to the output side of the alternator is the best way. This will make it possible to know exactly how much voltage is being generated by your Nissan. If the voltage reading is 13 volts or more, this part is operating as it is intended to. If the voltage is just between 12 and 13 volts, then a problem is occurring and should be investigated. If the voltage is less than 12 volts, then the engine is operating off of battery power and it is just a short time before your Nissan vehicle will not be able to run at all. If a voltage meter is not available, your Nissan alternator can still be tested to see if there is enough electrical power being generated to operate the vehicle. With the engine running, the headlights need to be turned on. If this causes the engine to pause or slow down, power is being drawn off of the battery to supply the electrical needs of the Nissan engine. You will also notice the headlights will not be as bright as they should be. As additional electrical components are turned on, the headlights will likely dim at an increasing rate. This can continue until the battery is dead and the engine dies if tested for too long of a period when the alternator is not producing over 13 volts. The only solution to a power supply problem is the replacement of the alternator. Recharging the battery can only supply the electrical needs for your vehicle for so long.