Desulfating a lead acid battery with the YIHUA 605D and Magnesium Sulfate

We’ve got a few “summer batteries” around here. By that, I mean they’ll start a car in the summer, but once fall comes around and temperatures start getting below freezing, all bets are off. Beyond that, we’ve got a collection of other batteries that just never made it in as core trade-ins.

And it’s probably a good thing too, because many of them can be restored.

One of the biggest early killers of 12 volt lead acid car batteries is sulfation. A battery dies, doesn’t get charged up again right away, and before you know it, sulfation has built up on the plates. This actually happens a lot here during winter, where a battery runs down fast, but because it’s so darn cold, it doesn’t easily charge all the way back up on short trips. The battery stratifies (sulphuric acid collects near the bottom with water collecting near the top), making the battery’s life even harder.

Here’s a video that mirrors much of the rest of the writeup here if you’d prefer…

…otherwise, keep reading!


The YIHUA 605D

In any case, we recently got a hold of the YIHUA 605D 60V 5A Digital Precision Adjustable DC Power Supply which looks strikingly similar to ARKSEN, THAOXIN, WEP, XPOWER, and MAXTRA power supplies of the same model. It’s a fairly cheap (about $100) power supply, and at that price I doubt I’d trust it to cleanly/accurately power sensitive electronics, but we got it primarily for recharging batteries and it does the job here well.

Unfortunately, the instructions are gibberish (I suspect it was run through poor Chinese->English translation software), so if you’ve got the same supply, or are considering it and haven’t used one before, here’s a crash course in usage:

  • the dials set the max voltage and max current. This may or may not be reflected in the digital readout you see on the unit.
  • the CV and CC (constant voltage and constant current) lights trigger when you’ve hit the limit you’ve set on the dial for that particular setting. So if CV is on and I see 3.5V on the readout, that means the dial for the voltage is set to a max of 3.5V and I’ve hit it. On the other hand if CC is on and I see 2.0 amps on the readout, that’s the current limit the dial is currently set to, and I’ve hit it with whatever device is attached. So to accurately adjust the max current or voltage, you pretty much need the corresponding light to be on.
  • Example usage: to charge a battery at 14.5 volts, disconnect the leads from everything. Turn the current to anything non-zero and the CV light should come on. Now you can adjust the voltage to 14.5. Hook it up to the battery – you’ll likely get a spark, so make sure you’ve got some face/body protection in case things explode. At this point, the CC light will usually come on (and the voltage might drop, though don’t adjust the dial because that would change the max without giving an indication as to what you might be setting it to). Turn the current up to whatever you’re comfortable with. As the battery accepts the juice (or if the current dial gets high enough), you’ll probably see the voltage start climbing back up until it caps at the 14.5V.
  • Note: The instructions claim that you shouldn’t run it at more than 60% of it’s rated load for extended periods. You don’t find that out until you’ve bought the unit. So keep that in mind.


The beauty of the charger compared to a normal battery charger is that it will allow an “equalization” charge, aka a “forced overcharge’. 15-16 volts is common for this (at room temperature). This is impossible to do on most of the car-battery-chargers in the automotive section of most stores.

The other benefit is that you can use it on other types of batteries too. 6V, 9V, 18V NiCd batteries can all be handled. And if you run into a 24V battery bank, this charger will do it.

The downside is that there’s no auto-shutoff. If you’re charging at a normal battery-charger rate (say 12.5-13.5V), assuming the battery takes the charge, you’ll get the current dropping to really low levels which is close to being off anyway. But if you’ve set it for an equalization charge at 16V and forgot about it for a couple weeks, there aren’t a lot of happy end scenarios.

The 605d was grabbed from It appears quite similar to the XPOWER 605D 60 volt 5 amp charger available on Amazon for around $110.

Since you’re not likely to need a 60V supply for car batteries, 30V 5amp models are available in the ~$70 price range, including the WEP PS-305D and various other unbranded units. Between Amazon and eBay, you should be able to find something that works.


YIHUA 605D - not hooked up to anything
YIHUA 605D - hooked up to a battery at 16V
YIHUA 605D - Still hooked up to a battery, but current limited.

From left to right: (1) The power supply set to 13.4 volts, not attached to anything. (2) Attached to a 12V lead acid battery, set to 16V. While the current limiting dial is set to something around 3 amps, it’s taking 0.86 amps at the 16V setting. (3) I’ve turned down the current dial to 0.17 amps, and you’ll see the constant current light is on – even though the voltage dial is technically still set to 16V, limiting the current resulted in a voltage drop to 13.6 volts.

Moving on – chemical desulphation via Magnesium Sulfate

For a bit of a primer as to what happens to a lead acid battery during charge/discharge, the Lead Acid Electrochemistry Wikipedia entry shows the equations (and a sulfated battery is basically when the discharged state doesn’t reverse)

Sodium Sulphate and Magnesium Sulphate are both commonly used for 2 things when it comes to lead acid batteries:

  1. As a replacement electrolyte (some people do conversions from Sulphuric Acid to one of these salts to bring “new life” to the battery, at the expense of total capacity).
  2. To desulphate the battery.

For #2, much of what you see out there is based on testing that was done in the late 1800’s. Some of the references I’ve found in doing some research are to The Telegraphic Journal and Electrical Review. If you’re interested, Google’s scanned these and offers them for free. Here are the links if you’re interested in some additional reading:

The formulas that described what they were seeing when using Sodium Sulfate (in Volume 20) were as follows:

H2 + Na2SO4   ->   H2SO4 + Na2
Na2 + 2H2O    ->    2NaOH + H2
2NaOH + PbSO4   ->    Na2SO4 + Pb(OH)2
Pb(OH)2 + H2    ->    Pb + 2H2O

Common names (I’ve color-coded to make it easier to match up):
H2 – Hydrogen
Na2SO4 – Sodium Sulfate (the salt you’d add)
H2SO4 – Sulfuric Acid (battery acid)
Na2 – Sodium
H2O – Water
NaOH – Sodium Hydroxide (caustic soda, lye)
PbSO4 – Lead Sulfate (what builds on the battery plates, causing a “sulfated” battery)
Pb(OH)2 – Lead Hydroxide
Pb – Lead

I suspect the reaction via Magnesium Sulfate aka Epsom Salt (MgSO4) instead of Sodium Sulfate (Na2SO4) should be similar, though I’m admittedly not a chemist. Do note that this was the series of reactions that seemed to explain what they were seeing back in the late 1800’s. So it may or may not be an accurate representation of the processes that hapepn – it just happened to be what fit.

Assuming for the moment it is accurate though, an interesting thing to note though is that the Sodium/Magnesium sulfate isn’t actually “used up” in the process – it’s recovered in step #3. So dumping 1/4 teaspoon in each cell should have the same effect as dumping in a tablespoon – it just might take longer.

Magnesium Sulfate can be found:

…with bath products at most stores, sold as “Epsom Salt”. Get the pure stuff (not scented, or with additives).

Sodium Sulfate can be found:

…on Amazon (US) for around $6-15 (1 pound) last I checked.
…on eBay, which is where I ordered mine.


Putting it into practise…

The following is the way that *I* desulfate batteries. That doesn’t mean it’s necessarily the best way, but it’s largely worked for me. Magnesium Sulfate is what I’ve been using, though I have some Sodium Sulfate on order and plan to experiment on a few batteries using that (as well as a mixture).

I’ll put this into a series of steps:

  1. Safety first. Full face protection is a good idea, and make sure all your skin is covered. Be in a well vented area (ideally outdoors), and ensure that there are no nearby sources of flame or spark. “What will happen if the battery explodes right now?” is something you should keep in mind during the entire process.
  2. Pop the caps off the battery. This is usually easy for low-maintenance batteries. Sealed (maintenance-free) batteries might require drilling some holes. AGM-cell batteries usually have a plastic cover that has to be snapped off, and rubber caps that have to be removed.
  3. Mix the Magnesium Sulfate (Epsom Salt) in some warm distilled water. You’ll have to “ballpark” the amount of water that you’ll need based on how full the electrolyte in the battery currently is. If the electrolyte is already well above the plates, you may not be able to add much water, so keep that in mind. As for the amount of Magnesium Sulphate to add, I tend to aim for 1/8 teaspoon per cell in smaller batteries (and for AGM’s), and 1/4-1/2 teaspoon per cell for typical car batteries. Make sure it’s mixed well and that all the crystals have dissolved.
  4. Use a dedicated syringe, or a tiny funnel to add your solution to each cell. Keep in mind that when you charge the battery, the electrolyte level will rise, so while you want the water to be above the plates, you don’t want it filled too high to the point where it’ll overflow during charging. If you’re using an AGM battery, you only want to saturate the mat (you don’t want it actually filling with a visible pool of liquid) – to do this, you’ll have to peek in each of the holes as you add and watch the glass mat’s absorbsion rate – it should act like a paper-towel (absorb fast when dry and slow when saturated). Once it’s slowed, you’ll want to taper off and stop.
  5. Gently rocking/shaking the battery can help the mixture disperse more quickly though it risks some electrolyte and acid splashing out. A better idea can be to wait – when you apply an equalization charge, the gassing should help mix things up anyway, and it should naturally disperse with time too.
  6. Assuming the battery’s already got some charge to it, apply an equalization charge to the battery – at room temperature this should be about 15-16 volts. Most people seem to recommend low current – anywhere from 0.25 amps to 1 amp. I’ve found that some batteries require higher charge current to keep the voltage from dropping below 15-16 volts, but try to limit the current if you can.
  7. Carefully monitor the battery throughout the equalization charge. Temperatures might climb – I’d stop charging if you start getting in the 30-35˚C range, personally, since the cells might be hotter than what you’ll be able to measure externally. The battery will also gas during the charge (since gassing will always have started by the time you get near 14.5 volts), which is not only very explosive, but will also deplete your electrolyte. You don’t want any sparks (even static) or flame nearby, and you may have to top up the electrolyte periodically during the charge.
  8. I tend to do equalization charges in 2-3 hour bursts throughout the week. A few reasons for this:
    • It’s easier to remember to check the battery frequently over a 2-3 hour period. If you decide to charge for 24 hours instead, there’s a higher chance you’ll forget.
    • The Magnesium Sulfate takes time to work. Chemical reactions don’t happen instantly. By spreading out the charge over a week, the solution will have more time to work, and you’ll agitate the solution via gassing multiple times throughout the process.
    • You’ll hopefully be able to see small improvements with each charge.
    • Less chance of the battery overheating when you limit the charge duration (even though you *should* be monitoring it anyway).
  9. Once everything is done, disconnect the charger and replace the caps. For an AGM cell, a few dabs of glue on the previous break-points will often be enough to reattach the cover. If you had a maintenance-free battery and drilled holes, fashion some plugs – ideally something that will allow venting if you managed to accidentally mangle whatever venting system was previously in place.
  10. The battery’s performance should now be improved! It might improve a little more down the line as the Magnesium Sulfate continues to work across further charge cycles. If you’re not seeing any improvement, you could try repeating the process with a little more magnesium sulfate, though 0 improvement would lead me to believe that sulfation wasn’t the problem to begin with (the plates may have deteriorated).

A few notes:

If you have a shorted cell, deteriorated plates, corrosion, or other internal physical “damage”, this won’t help. Shorted cells are usually easy to diagnose – if the battery wants to sit between 10-11 volts, that’s usually a telltale sign. Deteriorated plates on the other hand can have similar symptoms to sulfation – an inability to reach peak voltage, weak output, and low capacity. Note that AGM cells that have evaporated their electrolyte away and dried out the mat can exhibit similar symptoms.

Some people completely discharge the battery before adding the Magnesium/Sodium sulfate. Personally, I don’t go out of my way to discharge the battery first, since deep discharges are hard on the battery. I just add the sulfate to the battery at whatever-state-of-charge-it-happens-to-be-at and then charge from there.

One common theme amongst those who have used Sodium/Magnesium Sulfate is that when it successfully reverses the sulfation in the battery, the battery generally works fine until it dies from something else at which point it’s beyond recovery. This can be months later, or years later. So if you’ve chemically desulfated a battery to give it new life, the next time it dies, trying to desulfate again probably isn’t worth your time (the chance that sulfation is what killed it again is pretty low – it’s probably falling apart internally).

I’ve read a number of cases where people proactively add sodium/magnesium sulfate to brand new batteries to extend the life from the get-go (usually based on the notion that some battery companies in the past added sodium sulfate to more expensive batteries, and deep cycle batteries). I haven’t tried it, but if you have a new battery that didn’t cost much, it might be worth experimenting with.

Be big on safety. Even if you’re a risk-taker, at the very least wear some safety glasses – sometimes you can survive lead poisoning, sometimes a gash from an explosion doesn’t kill you, and sometimes you can grow back new skin – but you’ll never grow back new eyes. Even if you’ve done *everything right*, the battery could explode due to a poorly-timed internal short or a variety of other things.