Here is a magazine [Import Tuner] where they tested battery desulfators to see if they actually work [the verdict was yes]:
http://www.importtuner.com/tech/impp_1105_battery_desulfators_fact_fiction/
To put it in the simplest terms that I know how, as 12v batteries (cars, atv's, etc) age and become deeply discharged deeply too many times, they will often not take a charge anymore and people replace them. The science of it as I think I understand is that sulfate builds up on the lead plates, preventing them from passing (voltage/current?) and effectively ruining them.
Desulfators, in the most general sense, break up and dissolve or dislodge the sulfate from the lead plates, allowing the battery to be reclaimed. Not every battery can be saved, ie warped plates, shorted cells, but many Can be saved.
My understanding of why a typical battery charger won't charge a highly sulfated battery is the circuitry senses it is not taking a charge, so it quits trying. (Forgive my non-technical way of explaining this).
I have read that DC Pulses break up the sulfation. There are a lot of commercial desulfators. Most are hooked up to the battery itself and work from the battery's own power, but a charger is also required since the desulfator will eventually bring the battery down. Some of what I have read is these commercial units can take up to 4-6 weeks to bring the battery back.
That said, there are MANY circuit designs on the internet.
The reason I am interested in some designs over others is the amount of time it takes to reclaim a battery. 4-6 weeks is a long time, and I have 8+ batteries to try and fix. One commercial desulfator is $50 to $120 and on up, lots of them out there. Let's say I buy one for $75. They can't do multiple batteries at once. Let's say it takes 4 weeks to reclaim one. I am looking at 8+ months to process my batteries, or buying 8 desulfators, which financially defeats the purpose, you could buy new batteries cheaper than that!
I am not sure what circuit designs on google are "good" as you asked me for some circuit designs.
Googled the circuits: [battery desulfator circuit]
https://www.google.com/search?q=battery desulfator circuit&safe=off&rlz=1C1CHFX_enUS543US543&espv=2&source=lnms&tbm=isch&sa=X&ei=VYvzU4fGGJbtoATi_ICoAw&ved=0CAcQ_AUoAg&biw=1024&bih=619
Here is a 2 minute youtube video that shows the before and after of two batteries, showing the lead plates 1) Sulfated, 2) after desulfation :
[Inside view of lead acid battery before and after desulfator]
By the way, this desulfation process can work on all types of batteries. I have read where one guy is buying up discarded forklift batteries, reconditioning them, and selling them for a LOT of money. I understand forklift batteries are pricey. There is a lot of discussion for this process for people who have batteries for solar systems for their home, as having so many batteries, it makes lots of sense to save batteries when possible, both a benefit to your wallet and the environment. Anyway...