Last year I bought a switchable (contained on/off switch for outlets) USB adapter that plugged into the dash cigarette lighter receptacle. Using it, I noticed that it messed with some dashboard readouts. "Messed with" meaning it corrupted some dash board readings - I don't remember which ones.
Last month I bought a duplex lighter plug WITHOUT a switch for the same outlet and it worked fine. I suspected there was something in the internal switch wiring that caused circuit confusion in the Mazda.
I just bought a similar device for the cigarette lighter outlet in the center console that I'll be trying out in the next two or three days. Hopefully that will not encounter the same problem as before. I'll report back.

 

Many of those devices have "quality" issues.
Meaning, despite what brand you choose, it is often the luck of the draw if you get one that works correctly or not.

 

Yah most of them are junk.

 

Here's a switchable splitter that doesn't mess with my dash readings. It is installed in the center console 12 volt outlet in the new Android Auto device. I now have a couple extra USB outlets for charging - not for data transfer. I will run my fridge, vac or CB through this outlet plus phone charging and Necto temp sensor/alarm to keep my furry critters happy.

 

Your alternator only has so much capacity.
I hope you are taking that into account.
Otherwise, you'll be prematurely replacing a battery and an alternator.

 

Thanks. Not all used at the same time. It's great to have the fridge on a switchable outlet. And I have a (semi-accurate) SOC meter on the dash. Except for fridge, plugged in devices are low draw, like dashcam, Necto and GMRS walkie talkie. Dashcam is off when Necto is on. Fridge will sometimes be on an Echoflow battery.

On the topic of alternators, mine is over 7 years old. What is their anticipated life expectancy? What is the feasibility of a higher output alternator installed in a 2017 CX-5 Grand touring? Any other wiring or component switch outs required?

 

Average life expectancy is 6-10 years for the "average alternator", whatever that means, but that doesn't imply it is performing at optimum output.
At a minimum you'll need to replace both the ground straps and charge wire.
Mazda specific high output alternators can be found online.