Why won't my nissan altima start?

If it will start and run with a jump box connected and then die when you disconnect it means that the charging system is inoperative, your battery is too low to supply enough power to run the engine and everything else, even if a voltmeter shows good it still most likely will fail the load testing. Find a good independent shop that can do this because you don't want to mess up the computers programming.

Exactly, Gene is correct. When the alternator stops working the vehicle will continue to run off battery power only until the battery is dead. Most batteries have a 90 minute reserve capacity. This is the amount of time you can continue to drive, at night with the headlights on, and all other accessories (radio, heater, etc.) off until the engine stops because the battery is dead. Voltage and Cold Cranking Amps (CCA) are two different things. You need volts and Amps for the battery to work. I recently replaced the battery, which was eight years old, in one of my vehicles. It was having trouble starting, running, and was cranking slowly. Even though the battery had 12.61 volts it only had 90 CCA. It was supposed to have 630 CCA. Here's a photo of my load test results on that battery. Jim