Battery not charging

[PKRWUD]

It's not the battery. It's either the alternator itself (unlikely), or too much resistance in the circuit back to the battery (more likely). The battery really is just there for starting the engine. After that, it's no longer used (while running) unless the alternator's output falls below 12.6vdc. Once the engine is started, the alternator replaces the the energy the battery spent starting the engine, which usually takes less than 30 seconds. After that, the electrical system runs off the alternator, not the battery, so a weak battery shouldn't affect the voltage reading across the posts while running. Connect a DMM at idle again, and observe it while accelerating to 2000 rpms. What happens to the DMM?

Take care,
-Chris