The alternator is rectified but not one million percent.
A tiny bit of AC gets through.
On 2nd generation Dodge Cummins trucks it’s a common thing to have too much AC ripple cause torque converter erratic lock/unlock issues.
“Slowly killing your alternator” by using it is silly. It’s there to make power.
You’re slowly killing your tires when you drive the truck, and they cost a lot more than an alternator.
If you’re concerned about wiping out your ECM with AC ripple just touch your DVM leads to your battery every now and then and keep an eye out for it.
I have the 2-gauge cables from my truck batteries to my two camper batteries setup, and it works great. You can theorize all day, but my alternator isn’t fried, my batteries charge great and my AC ripple is at about .02VAC last time I checked, and since I own a 2nd gen Dodge Cummins I do have a look at that now and then.
And really, even if I did have to put on an alternator every couple years I’d still do this. It works too well to not do it.
