1998 Nissan Maxima car wont stay running

Suspect the charging system, specifically, the generator. Charge the battery at a slow rate for an hour, then measure its voltage. A good, fully-charged battery will read 12.6 volts. 12.2 volts indicates it's good but discharged. The engine will start and run on the battery long enough for the next test.

Measure the battery voltage while the engine is running. It must be between 13.75 and 14.75 volts. If it is low, the generator is the main suspect but there are other tests that should be done first to rule other things out.