I have a couple of batteries that won't take/hold a charge.

I've heard anecdotal evidence about desulfation but have no direct experience nor do I know anyone that has.

I'm curious enough to try it, but need some real-world input on the process and the equipment required.

As I understand it requires a hard, high current charge of above 15v. You need a way to give the battery this much current.
This is good for lead acid battery's only. Most AGM battery's can not be done, except Lifeline battery's.

It’s a low current (under an amp) and higher voltage (15volts and up) applied for 24 hours or more (days even). It can be pulses or continuous.

It’s supposed to dissolve sulfate crystals off the lead plates and back into the acid solution.

What kind of charger are you using?

A lot of the digitally controlled chargers won’t try to charge a battery if it’s under a certain voltage to begin with. The trick is to hook a good battery up in parallel with the discharged battery to trick the charger into turning on and then disconnecting the good battery after a few minutes.

As far as equipment required, you’ll need a charger with that capability built in. I had one for the house batteries on my sailboat.

I used a "Battery Minder" for the V-Tail. Kind of pricey, but when aircraft batteries cost three hundred bucks and more, getting an extra year or two from a battery pays off.

I believe there are lots of videos on Youtube.

If you spend a little more money than chump change for your typical hardware store battery charger, you can buy a middle of the road charger with built-in chip controlled save my old sulfanated battery from certain death function, with other functions as well to recondition a near death or just low battery using built-in auto-sensing algorithms and charge rates. It's really pretty impressive. I have one and have been using it for a few years now with outstanding results. I don't recall the price but it was prob less than $150.

I would be careful about what you choose to try based on youtube dudes bringing back batteries from the dead. If you can't do it with a bona fide major brand name reconditioning/charging device, I'd pitch the battery, unless you're using it for racing lawnmowers or an old tractor or golf cart. I wouldn't put that in any modern vehicle with computer control.

Google says this:
The desulfation process is a 24-hour cycle during which the charger emits a high-voltage, high-frequency, low amperage pulse into the battery. This pulse is designed to knock crystalline sulfate deposits that have built up on the battery's lead plates, back into solution.

More than I wanted to know at this link.

My Napa branded battery charger/jump starter has an automated disulfate function that worked on one occasion and failed on another...

I once saw a Youtube video where a guy used a welder to bring back some dead batteries... I'd like to say I wouldn't try it... but if we are being honest, with the right set of circumstances (and at least a modicum of safety precautions) I'd give it a try in a non-vital role battery.

Cause science is coooool

I'm not versed enough to explain it as well as I'd like so, I'll just add that I purchased a NOCO Genius 10 Smart Charger that has a 'Desulfator' function, and though I have not used that particular function (I purchased it earlier this year primarily because I needed the capability to charge AGM Batteries), I'm REALLY impressed with this charger! AND it's currently 20% off on Amazon!

https://www.amazon.com/dp/B07W3QT226

For years I've been using the same Battery Minder chargers as V-tail. I can't add any additional information regarding their operation that hasn't already been posted but my personal experience is that where I used to get 5-6 years from automotive batteries and 2-3 years from lawn mower batteries, since using these float chargers/desulfators I've been getting 7+ for all batteries. And this is for different brands - Motorcraft for car, CAT or NAPA for truck, Wal-Mart Everstart for mowers.

I have used other brands of float chargers w/desulfator in the past but like the Battery Minder for their ability to adjust charge to temperature. I think the NOCO and others have this feature as well but my Optimate and other one (can't remember the name) don't and over a long period of time I found I needed to add water to batteries that were on those chargers.

Certainly there are other variables that could account for the water drop but one automotive battery I bought new and wasn't installed (kept in the house), checked to make sure water levels were correct, then put it on the Optimate 5 and didn't touch it for 1.5 years. When I checked it again at that time all the cells were down by about half. Just food for thought.

Let us know what you get!