Sodium Sulfate Salt (Na2SO4)
Lead-Acid Battery Longevity Additive

Adding Sodium Sulfate to a new or newish lead-acid battery is reputed to extend its life by around 3 or 4 times, and, with treatment and cycling, to often restore years of good life to old, "worn out" ones. There's one set of instructions for new(ish) batteries (best time - just dump in the salt), and another for renewing "worn out" batteries (dump out the the crud and the acid and replace it with distilled water(!) and salt, then cycle it a few times).

If a battery is somewhere in between newish and worn out, guidelines are uncertain. Just adding the salt to a much used battery can cause it to short out, in which case it's ruined. My feeling is that for a mid-life battery, it's probably prudent to leave it until it needs renewing, or if the renewal process seems like too much bother or too much risk, to leave it and add the salt to your next new battery.

Disclaimer: I will not accept responsibility for anybody's battery(s), or for injuries resulting from battery handling or contact with acid, or any other problems resulting from use of this free information. I hope this information may prove valuable, but nothing in it is guaranteed to be correct, or appropriate to any given situation. The salt and salt kits are not sold for use as a food or medicine. Warranty for them is limited to refund of purchase price. BE AWARE AND BEWARE OF THE HAZARDS OF LEAD-ACID BATTERIES AND THE CORROSIVE SULFURIC ACID THEY CONTAIN. ALWAYS WEAR GOOD EYE PROTECTION AROUND ACID, ALKALI OR OPEN BATTERIES.

* Treat New(ish) Battery for long life
* Restore "Worn Out" Battery
* Treating "sealed" Batteries with Glued-on Lids
* Sodium Sulfate Kits for Sale
* Chemistry

* Sodium Sulfate is reputed to extend the life of new lead-acid Batteries by 3 or 4 times, and, with cycling, to restore some good life to old ones.

* Sodium sulfate should be chemically superior to sodium-aluminum sulfate or potassium-aluminum sulfate ("alum") for these purposes, and much better than magnesium sulfate ("Epsom salts").

* Alum is nonetheless effective, and has been added to some 6 volt golf cart batteries - hence their notable longevity over other types, such as 750 charge-discharge cycles versus a typical 120.

* It's been reported that Interstate put sodium sulfate in their Optima batteries (originally designed by Hot-Rod Magazine in about 1990). But evidently they have stopped using it: At an electric car company, I learned that some "prototype" Optima batteries had lasted 5 years in daily electric vehicle (EV) use. Optima batteries delivered later lasted only "the usual" 1 to 1-1/2 years.

Sodium Sulfate "Kits" for Sale

I was having trouble getting sodium sulfate locally and I finally ordered a 30 Kg keg - the smallest size I could get on the web - of high quality anhydrous sodium sulfate USP. Naturally, this is far more than I need, so I'm selling the surplus in smaller quantities for others who may also have the same trouble.

Kit Includes: Anhydrous sodium sulfate, 6 Dixie cups (one for each cell), battery label. (So you don't add it twice!) please refer to or print this page for instructions.

Optional: 6 rubber test tube stoppers (for batteries with glued-on lids - see instructions): add $4.

Price List:

100 grams - $7 (small car batteries 28-34 pounds)
120 grams - $8 (medium car battery 33-40 pounds)
165 grams - $9 (typical 45-55 pound "size 27" deep cycle battery)
330 grams - $15
660 grams - $23
1 Kg - $30
2 Kg - $50
5 Kg - $100
10 Kg - $170

Salt quantities required in a battery are "ballpark".

Craig Carmichael           Craig
820 Dunsmuir Road          @
Victoria BC        
Canada V9A 5B7

250 384 2626 (Pacific Time Zone)

By Mail: Up to 660 grams, please add $10 to price of merchandise for postage & handling. Above that, please enquire, giving Canadian postal code, US state or zip code, or country.

Pickup: "Cash and carry".

Payment: Paypal, cheque, Canadian or international money order, cash. Canadian funds. (will accept $US cheques or $US cash at par.) Note: You mail cash at your own risk - put it inside folded paper, no coins. (I'll try to ship within 72 hours.)

The ballpark amount needed to treat a battery is about 1 gram per cell for each 2 pounds of battery weight, up to 3 grams per 5 pounds. For example, a 50 pound battery should have about 25 to 30 grams per cell, total 150 to 180 grams. (Double per cell, same total, for 6 v batteries.)

Notes: This treatment is for typical "FLA" (flooded lead acid) batteries such as car batteries and marine/RV deep cycle batteries. Many 6 volt golf cart batteries, very large "traction batteries", and (doubtfully) Interstate "Optima" batteries, may already have alum or sodium sulfate added to them. Adding more probably won't help and might hurt. Most batteries under 60 pounds, unless otherwise indicated, are sold with none added. Note that gel cells may not be amenable to an addition of salt. Batteries with glued-on lids need to have small holes drilled in the "solid" side of the top, which are plugged with rubber stoppers (eg, 1/2" holes, #00 solid test tube stoppers)

Treat New(ish) Batteries, How-to

: ALWAYS WEAR SAFETY GOGGLES OR (better) A FULL FACE SHIELD WHEN OPENING A LEAD-ACID BATTERY AND WHILE IT IS OPEN. Wearing rubber gloves and clothes you hate are also recommended.

The easiest way to add the salt is to divide it equally into 6 small containers (eg, the six paper cups that come with the kit), and then pour one into each cell, through a funnel or by forming the paper cup rim into a "spout", noting which ones are done and which not. Mixing by tipping the battery gently back and forth (after closing it) is desirable. Regardless, it will soon dissolve. This is a good time to check the water level in the battery. If any cell seems lower, or if the tops of any plates are out of the liquid, add a little pure water to top it up - distilled water is recommended. (Keep the funnel, if used, out of the acid - if you get the tip wet, the salt will clog and stop pouring.)

Restore "Worn Out" Batteries, How-to

: ALWAYS WEAR SAFETY GOGGLES OR (better) A FULL FACE SHIELD WHEN OPENING A LEAD-ACID BATTERY AND WHILE IT IS OPEN. Wearing rubber gloves and clothes you hate are also recommended.

The procedure here is more involved than for a new battery - a good reason to simply put the salt in the new battery before it's used. (On the other hand, it's easy to find free used batteries at this time! so far! ...and reusing them is best for the environment.)

First, the battery must be emptied. Outdoors is much the best place. I shake it and turn it upside down within a big plastic storage container. The acid and the lead crap goes into the container (which I use for nothing else). You should be well protected for this. (Once I dropped a battery in and acid (from several batteries) splashed out! Beware! I was wearing a full face shield, rubber gloves, rubber boots, and a jacket. As soon as I could I threw my (old) clothes in the washing machine and had a shower.)

If a lot of black crap comes out, you may elect to pour some water into each cell, shake, and dump it again. Remember this is poisonous lead compounds, and that lead poisoning builds up in the body and is slow to disperse. Acid and lead - great combo!

When the liquid clarifies in the container WITH THE LID ON IT and a WARNING SIGN, with the lead stuff settled to the bottom, I gently pour the acid into some other container (leaving the lead behind), and neutralize it with alkali. (Opposite of acid -- another dangerous, corrosive substance to beware of! KEEP YOUR PROTECTIVE CLOTHING ON!) Add it slowly. Stir. It bubbles. If you add a lot at once, it gets hot and can boil. Don't melt your plastic pan! The gas that comes off is (I believe) sulfur dioxide - another good reason to do it outdoors. I generally use potassium hydroxide (caustic potash). Sodium hydroxide (caustic soda) should also work (or lime?). These are available at various odd places - soap making, farming/gardening, drug stores... Oven cleaner is essentially dissolved sodium hydroxide. Leaving it just slightly acidic (pH 5 or 6) is preferable. It stays at pH 1 "forever", and then a slight bit more alkali and suddenly it's too high. The only warning is the reaction gets less vigorous as the acid weakens. (Save a cup or two of acid to pour back in to be ready for this.) You need cheap pH test paper strips from a science/lab store. At this point, the liquid (water) and the salt (potassium, sodium or calcium sulfate) is biodegradable and can be tossed out somewhere.

The lead crap is still a problem. I try to find a really bad battery - shorted cells or whatever - to take for recycling, and pour it (minimal liquid) or dump it into that. It's just more of what it already has in it, which the battery recycling places presumably turn into new battery material.

Now (if that hasn't scared you off completely), back to the battery.

Take somewhat less distilled water than the amount of liquid that came out of the battery. (or at least, not more. Britta filtered tap water is good enough in some areas.) Fill a sink or container with hot tap water and set the distilled water container in it. Let it warm up. The reason for this is that sodium sulfate is far more soluble in warm water than in cold. (33ºC is max. solubility) Once it's warm, while stirring or shaking the container, slowly add the sodium sulfate powder to the water. If you put in too much at once, if you don't stir, or if the water is cold, big lumps can form, and they take a vexingly long time to dissolve. Keep agitating until the water more or less clarifies.

There's always more to be said, and different opinions. There are a number of web pages about renewing lead-acid batteries to be found. A university professional offers this advice:

"Quote the addition rate as a percentage (it looks like you are using about 5 to 6% - 165g in 3L). 
Then when people empty their battery out and transfer the acid to a storage bottle they’ll know
the total capacity and can make just the right amount of the right strength solution."

(Something to do might be to figure out a good specific gravity of salt solution.)

Then, add the water in equal amount to each battery cell until the water is gone. Be careful not to lose track of how much you've added to each one. Top up the battery to the desired level with more distilled water. (at least cover the plates!) (Amazingly, this renewal procedure has also been done with pure water only, no salt. Of course, that won't give the longevity.)

Close the battery. It's now ready to be cycled, charged and discharged several times to complete the renewal process, which may take a few days. Here are cycling instructions from someone who's done it many times with alum salt. You need a voltmeter unless your battery charger can show you the voltage:

* Charge at 5 amps, let trickle down over night.
* Discharge down to 8 volts (4 volts for a 6 volt battery).
* Recharge/discharge 1X more.
* Charge third time and it should work well.
* Forget all the testing. You will go nuts.

A comment: After the first charge and discharge only, (and or perhaps right after filling) I have found it useful to discharge it completely, to 0 volts - to short the leads once it's very low - and leave it shorted for an hour or two. This especially helps if the battery won't supply much current and dies quickly.

The person who gave these instructions also said he doesn't bother trying to restore a battery unless, after a bit of charging, it will hold 12 volts for an hour, and that then his success rate is 9 out of 10 restore successfully. (I suspect that if it soon drops to a lower level such as around 10 volts, it probably has some sort of bridge between a "+" and "-" plate within a cell that keeps discharging it.)

Load graph of a battery after treatment.
(Cycles 3 and 4 were virtually identical. Voltages,
though below average, continued to rise gradually in cycles 6 to 9.)

Treating Batteries With Glued-on Lids

A professional advises that rubber stoppers as shown below "always" leak after a while. Their procedure is to drill 1/4" holes, and to use a glue gun (heat glue) to seal the holes. ("never leaks.") I guess they stick in a small rubber hose to fill the battery.
One might also simply wrap the battery, all the way around, with a few turns of electrical tape over each stopper to prevent it from coming loose.

"Sealed" battery. I found that holes seem to be very easily drilled for each cell through the "solid" side of the top. These are plugged firmly with rubber stoppers. The dividing walls between the six cells are usually visible on the sides.
These are 1/2" holes and #00 solid rubber test tube stoppers.
You need a small funnel to fill the battery.
WEAR GOOD EYE Protection (at least!) when drilling,
and when working around any open battery! The acid is dangerous.

Note that there are pressure relief holes in the glued-on lid section - it's not actually "sealed", so there should never be pressure inside to cause the stoppers to pop out... unless one or more of the vents are blocked.

Chemistry - How it works

The sodium sulfate turns into sodium bisulfate in the sulfuric acid:

Sodium Sulfate:        Na2SO4  (pH 7 - neutral)
Sodium Bisulfate:      NaHSO4 (pH 1 - strongly acidic)
Sodium Bicarbonate: NaHCO3 (pH 10 - mildly alkaline)

Sodium bicarbonate (baking soda) can be used to clean battery electrodes, but only when the battery is drained. Sodium bisulfate is an acidic "baking soda" compatible with the battery acid, so it can be left in the battery as an additive, to keep it clean while it is in use.

How restoring "worn out" batteries works:

The problems with untreated batteries are that the plates gradually collect sulfate which electrically isolates areas of plate, gradually reducing battery capacity, and that as the plates corrode, lead compounds accumulate on the bottom of the battery as a black powder, which can build up until it touches plates and shorts a cell.

The first step in restoring, dumping and cleaning it out, removes enough powder to prevent shorting. Replacing the acid with water sounds absurd, but a lot of sulfate from the acid gets converted into lead sulfate on the plates, so in fact, there is still a considerable amount of it in the battery after it's dumped. In fact, since the battery is "worn out" with the plates so sulfated it won't hold much charge, there's about enough sulfate on the plates to charge and discharge the battery. With the charge-discharge cycling, this get cleaned off the plates and converted. First, the sodium sulfate is converted into twice as much sodium bisulfate, then most of the rest is converted back to acid as the battery is cycled in the restoration process. The electrolyte of the restored battery usually has a much lower specific gravity (SG) than usual, seemingly about 1.1 instead of 1.25 when charged, but it works.

Shorted Cells (a theory of explanation):

I suspect the reason cells can get shorted if salt is simply added to an older battery is that along with lead "crap" accumulating on the bottom, lead sulfate bridges can form between plates. These are "benign" electrical insulators, but with the battery renewal they are desulfated to lead and lead oxide, which are conductive. Then they become low resistance links between the "+" and "-" plates. The more the battery is charged, the lower this resistance becomes and the faster the cell discharges again. Unless there is some way to remove the bridge(s), the battery is toast.

If the acid is drained and replaced with distilled water containing sodium sulfate, probably the sulfate is taken up and the bridge is dissolved in the initial fill. Once it's become lead and oxide and the salt prevents further sulfation, this doesn't work. There may be some way to dissolve them, perhaps by refilling with acid only and giving it time (months?) to resulfate, then doing the renewal procedure. This is all speculation - I haven't actually opened any batteries to inspect the plates.