Try one of these in the correct size.
The battery was a fairly new one (Jan of this year, nice Duralast Gold yadda yadda, but was junk. They swapped it immediately.All you can really tell with a scan tool, and not all may be available:
1) Is a charging fault set? Codes may not even exist depending on the car.
2) What is current system voltage?
3) What is commanded/target/set point voltage? For instance a Kia may charge at 12.3v idling and be 100% as designed.
4) What is the commanded duty cycle/output/whatever? How hard is the PCM trying to command this alternator? Going 100% wide open with no charging? Does the PCM even know there's a problem? Is the PCM even who is in charge of the alternator?
Other than that you'll need to do a basic voltage drop/big test light test on the B+ cable and the block, and check inputs into the alternator on the electrical plug.
Yesterday I had a dead Rover, bad alternator. B+/B- good with big *** test lamp, good enough it should charge something. Single wire alternator, LIN bus communication, scope shows a pattern of "something" which look like good data packets. Replace alternator.
Then an Avalon, also bad alternator. Big *** test lamp confirms cables/block acceptable, 4 pin connector. 1 constant B+ feed, one is switched, both good. Another for the warning light, don't really care about that. The last is a PWM signal at key on engine off, pulls down to ground upon starting which I assume is full output. Replace alternator.
The problem learning a scan tool, is you/me/nobody knows what data is inherently in it, or how to find it. So you try to find the info you can and do with it what you can. I didn't know the LIN bus on the Rover was 0-12v, or ground was full output on the Toyota. But looking at charging commanded output, actual output, and duty cycle to the alternator made it more apparent how the system was designed. The voltage plunged after startup so I wasn't convinced to bother doing a voltage drop on the alternator cable, it was clear there was absolutely zero output. I always do that test engine off, so a charging alternator won't fool me the cable is bad.
Typically, typically, if the red battery light is on, you have some issue. If it isn't, the PCM is generally okay with the charging system function. But the toyota had no charging system light on at 11 volts at idle. So who knows.
By my multimeter and the Autel it's running 13.5V even with a load (high-beam/AC/Radio), so it seems like it's regulating and charging...
...but possibly marginal? Everything seems to say 14V +/- is where you want to see it.
That's not the right tool to test a alternator, if you want to see charge cmd rate and actual output rate yes but, that's not a thing on a Mazda 3.
It seems like some of the newer scanners will give you the OE spec. The Launch scanners can have a BT unit hooked up to the battery for testing (this appears in the Icon line, but only the T10