I assume that you disconnected the jumper cables as soon as the car started. If your alternator is not working properly on your vehicle, it will be unable to recharge your battery as the car runs. The vehicle will run until it simply drains the battery again. To properly test the system, you should begin with a fully charged battery and then check for alternator output by measuring the voltage at the battery terminals with the engine running. This voltage should be greater than 13.5 volts. Any less than 13 volts indicates that your alternator is not functioning.
will do that thanks