How do you know the alternator is going?

Hello, It sounds like your battery is too low in charge or unable with the current load carrying capacity to crank the engine as needed. Before doing anything or guessing it anything else, the battery must be tested for state of charge and the ability to sustain a load. If it is fully charged and holds under load by a tester, then you move onto the next time. The next thing could be a transmission range sensor not showing park or neutral. It could be a starter motor. It could be a starter signal wire and terminal at the starter solenoid. It could be a cable issue. There are several possible causes of concern to be investigated. If the battery is found to be able to sustain a load but is too low in charge, you could have a charging system problem causing the battery to lose its state of charge. In order to test this you will need to put a known good battery with a full charge in the vehicle and then evaluate the charging system with a voltmeter or charging system tester that can measure alternator output in voltage and amperage. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops