2004 neon changed battery and alternator still not charging under load

Make sure the battery has a full charge and connections all good. If the battery is down you can't do any testing. What testing have you done? Any applicable trouble codes for battery or charging system? The generator bat terminal should be hot all the time, even with key off, use a test light and see if any voltage there. If nothing, could be problem with wiring circuit or fusible link. You charging system is computer controlled.

The battery light is on and charging low. Replaced battery, alternator, still on. Replaced PCM and ignition switch and immobilizer. Still battery light on. How to get it off

Check your battery heat sensor. There is a wrap that goes around the battery and then a sensor that goes in the wrap. If the sensor is bad it will cause your battery light to come on. As far as the charging goes I don't know because I have the same problem.