Have looked around a little bit, it seems that the "conventional" wisdom is that we don't have to worry about desulfating conventional lead acid batteries, that it is only important on larger batteries, such as marine deep cycles, forklift, etc.
Just blindly looking at another forum (not as active as permies), found a post about it, along with the following information (copy/pasted and giving credit via link to OP).
It looks like the person who created the charging device linked below is efficient at increasing life of most batteries through this technique. Any thoughts/opinions/comments on desulfating in general? My opinion is that the people who say we shouldn't are from the battery mafia (similar to the CFL mafia).
While I linked to a specific device (open sourced), would welcome any information about similar devices that do the same thing.
Capacitive Battery Chargers
Postby dave brenneman » Sat May 19, 2012 5:31 pm
Many of you will remember [Mikey Sklar] from the multitude of times he’s been on hackaday. What you may not have noticed is that he is an ubergeek, living off the grid.
He has Solar PV battery bank, three electric vehicles, a shipping container loaded with battery powered tools and a small army of iRobot Roomba’s for cleaning. Getting the maximum lifetime out of a battery by removing sulfation is essential to keep expenses down.
Keeping expenses down is nearly a full time job when trying to live the homestead lifestyle. Our current culture makes it extremely difficult to survive completely on self made/grown things and bartering. They seem to be doing pretty well though. One way he can reduce his costs while still getting to enjoy some modern gadgets is to get longer life out of his batteries. He does this by using a capacitive battery charger and desolfator that he designed and affectionately calls “Da Pimp”. He also brings in a little bit of income by selling kits!
A capacitive charger behaves like a constant current power supply dynamically adjusting the voltage to get over the batteries internal resistance. Plus there is a pulse from the AC/DC conversion. This allows for old batteries to last longer and for dumpster dived to be used as replacements. Capacitive chargers are small, silent and super efficent (up to 60% more so than cheap transformer based chargers).
Of course, [Mikey] is a supporter of sharing information so you can also go to his site and download the schematics,bill of materials, gerber files, and files for the housing, to build one yourself.
Da Pimp is a extremely portable battery tester / desulfator / charger.
It uses capacitors instead of a transformer creating a highly efficient conversion of AC to DC voltages. It is available fully assembled with all accessories or as a complete kit that requires soldering. Da Pimp is ideal for the following:
rapid testing of batteries to determine how sulfated they are
recovering lead-acid car starting batteries
recovering marine boat batteries
recovering entire sets of lead-acid deep-cycle battery banks ( golf carts, forklifts, other electric vehicles and pv solar systems )
recovering power tool batteries (drills, weed wackers, saws)
recovering iRobot batteries (vacuum / mopper)
The design is completely open with source code, schematics, circuit layout and bill of materials all made available.
The comments from the Hackaday link indicate there are some improvements that could be made to the circuit, but something like this might prove useful as a starting point for homesteaders/reusers/recyclers
And a worthwhile coment from Hackaday:
May 19, 2012 at 12:18 pm
A “theory of operation” would be nice, to determine what this actually does without reading both schematic and software.
Best I can tell from looking at the schematic alone:
Lead-acid: Should charge well. May desulfate to some degree. Non-conductive sulfate deposits on battery plates need higher than normal charging voltage to dissolve. This is achieved since the capacitive coupling allows the voltage to rise to required levels if battery resistance is high. But as small patches become desulfated, resistance quickly drops to the point where it’s not feasible to desulfate the rest of the plate area; so this is only a partial recovery. Better than nothing though!
NiCad: Possibility of overcharge due to the NiCad’s slight negative dV/dT when fully charged. Bad NiCads are the opposite of lead acid – they’re low-resistance due to shorts caused by the growth of conductive crystals (whiskers). A high current pulse is needed to shatter those whiskers; typically supplied by charging up a large capacitor with rectified AC, then dumping it quickly into the battery. I’m not sure if it attempts to do that, but the capacitors are too small to be effective in my opinion; I’ve had the best luck with a 330uF photoflash capacitor.
NiMH: Stronger possibility of overcharge due to the larger negative dV/dT when fully charged. NiMH has no repairable failure mechanisms.
Li-Ion: Mikey gave a safe answer – no. I agree with this. Highly experimental at best.
Since the idea is to extend battery life, I’d stick to lead acid. Maybe NiCd/NiMH if no better options are available, and the charger is programmed to slightly undercharge.
I do love the simplicity, efficiency, and economy of capacitive charging. Well worth considering for hobby projects. Just remember that it can produce dangerously high voltages, with no isolation from the AC line. That’s why you don’t see it in many commercial products, especially if they’re not entirely self-contained.