Please let us know what you found.
This has the symptoms of an alternator with low output at idle, certainly.
While low alternator output is suspected, some alternators used a diode trio to generate the idiot light voltages, and if those diodes drift in value (and they very often DID) , you will get the appearance of a defective charge rate when nothing is really wrong. Dont know if Mazda used such a system, but it is worth mentioning.