Dodge Stratus: Battery Light ON!

There should be a trouble code set if there is a charging system problem. See what the computer "thinks" is wrong.

But even that won't give a complete diagnosis. You need to determine:

a) is the alternator producing sufficient current at the correct voltage and the light is a false warning b) if not, is the alternator field receiving the proper excitation current from the regulator (inside the computer). c) is all wiring intact, and are all connections good?

The following tests should be done when the warning light is on:

a)Put a voltmeter on the battery with the engine running. It should be in the neighborhood of 13.6 volts (no electrical loads turned on) and shouldn't drop more than a tenth of a volt or so when you turn the headlights on. Furthermore, the voltage should come back up if you rev the engine slightly. You can also remove the alternator and have it tested at an auto parts store, but this test is nearly as good.

b) if the alternator fails test "a", then check the field terminal voltage at the alternator with the ignition in the "run" position (preferably with the engine running, but be careful of moving belts and spinning pulleys). If its getting battery voltage there, then its most likely an internal alternator problem, OR a wiring problem between the alternator and the battery. To rule the latter out, shut the car off and measure the voltage at the large "Bat" or "B+" terminal on the alternator. It should read equal to the battery voltage. Ideally, you should also clip a test lamp there because high-impedance voltmeters sometimes will read normal voltages across very bad connections, but current won't flow when a load is applied.

c) if it comes to it, trace the wiring out.

Sounds similar to my 93 Caravan 3.3 (now fixed). Intermittently, over a period of a couple of months, rarely at first, more often towards the end, the Battery light came on. When a restart would not correct it, I found a slight tap in the alternator connections would do the trick. It made me think at first there was a bad/dirty connection at the alternator. Cleaned them all up, but problem persisted. Toward the end it was happening, as you mention, every, or every other trip, and tapping alt to restart output was getting more severe. When battery light was on, code 41 (Generator field not switching properly) was active. All tests on alternator when code was not active and Batt light not on were normal, volts and amps output in limits. When code was active and Batt light on, alt had 0 output.

Alternator replaced - no problems since, 5 months ago.

Probably just the brushes. When they get worn down pretty far, their springs don't hold them tightly enough against the slip-rings. You can replace them in a Nippondenso alternator with a phillips screwdriver. They cost about $10.00 from an alternator rebuilding shop.