I needed to add a bit of water to some of my SLA's so I went to Publix grocery store and bought a gallon of DISTILLED water.

After adding it to several of my batteries, I measured reduced capacity that got worse over the next few weeks on all of them. Finally, 3 out of 4 of the batteries I added this distilled water too have lost so much capacity as to be junk batteries now.

After some research, I found out that "Distilled" water doesn't guarantee ANY level of purity. Just that it's been "Distilled".

Apparently, you have to be more careful than just buying generic distilled water when filling your LA batteries or SLA batteries. I ordered a TDS meter which should arrive soon and I intend to check future purchases of so called "Distilled" water with that meter. I have found that for batteries, the PPM should be no greater than 5 PPM.

Fortunately, I do own a Reverse Osmosis kit for making emergency water so I can get really pure water that way.

This is just a heads up in case you find yourself wanting to fill Lead Acid batteries with water and think that all you need to do is run down to the nearest Walmart or Publix and get a gallon on "Distilled" water.

 

I ordered a TDS meter which should arrive soon and I intend to check future purchases of so called "Distilled" water with that meter. I have found that for batteries, the PPM should be no greater than 5 PPM.

I've never seen anything but conductivity used for gauging water quality. Is this what your meter uses, but reports in TDS?

This is just a heads up in case you find yourself wanting to fill Lead Acid batteries with water and think that all you need to do is run down to the nearest Walmart or Publix and get a gallon on "Distilled" water.

I'm a little surprised that any small impurity in "distilled" water could be at a level high enough to affect a battery. Plenty of people have taken the shortcut of adding tap water and have gotten away with it. Something's odd here.

What led you to add water in the first place?

 

I've never seen anything but conductivity used for gauging water quality. Is this what your meter uses, but reports in TDS?

I'm a little surprised that any small impurity in "distilled" water could be at a level high enough to affect a battery. Plenty of people have taken the shortcut of adding tap water and have gotten away with it. Something's odd here.

What led you to add water in the first place?

I have a lot of lead acid batteries and I was just in the frame of mind to do some maintenance on them....checking them for elecrolyte etc.
Two had been in use for quite some time and were down to about half their new capacity but still worked. They looked low on electrolyte and it's true that batteries do dry out after a long time in use. Even sealed lead acid batteries vent some moisture. After adding the distilled water they showed a definite downhill plunge in capacity.

I can't account for it any other way except the water that was added.
Obviously adding water changes the chemical balance. Some say sufuric acid doesn't evaporate.....I question that especially during higher power desulfation processes. Maybe the added water diluted the H2SO4 balance? I could "experiment since they're junk anyway buy adding small amounts of H2SO4 and see what happens.

Maybe the batteries that took a big hit were already somewhat compromised.
Still, even if it's not noticeable right away, it might be best to make sure the water you're addiing is actually 5 PPM or less.

 

fter adding the distilled water they showed a definite downhill plunge in capacity.
I can't account for it any other way except the water that was added.

You just diluted the concentrated acid on the remaining (reduced) reaction surface. The water was likely just fine. The batteries were likely already partly bad from low water levels revealing reaction plate surfaces to air.

 

As we can only now get De-mineralised water here now in hardware shops, I collect the water from my indoor demumidifier, seems to be fine for topping up batteries.

 

What do you guys think about adding VERY small amounts of battery acid back to the battery?

 

Well,
I went ahead and added a VERY small amount of Sulfuric acid to one of the batteries that took a sharp nose dive after adding distilled water.
About 10cc to each cell.

It's an experiment and I have a device for accurately measuring capacity down to a tenth of an Ah so (actually 1/1000th of an Ah?) if it improves I'll know for sure.
I've have several detailed discharge / capacity curves already logged for this particular battery. Here's some of the past data on this battery......



And for reference, I charted the capacity curves so I can compare what happens AFTER the acid was added.....



Right now it's back on charge. I'm using an OptiMate 4 Desulfating Charger
The Jury is out....we'll see what the verdict is soon.
Did adding H2SO4 restore any capacity or did it ruin the battery????
TBH, I'm very curious myself.

 

According to an article I read by Exide who are a major battery manufacturer, only the H2O evaporates, leaving acid in the battery and you should never add additional acid as it eats away the structure if its too strong. May be worth looking up evaporation of H2SO4 and see what you can find out.
(also known as oil of vitriol) I think it readily absorbs moisture in the air.

 

What do you guys think about adding VERY small amounts of battery acid back to the battery?

This could raise the specific gravity too high, cause a stratified battery in which the acid concentration is not equal if not properly mixed and excessive positive corrosion but I've done it to extend life of an already sick battery bank. If the plates were exposed they won't completely come back unless you have a industrial battery with removable plates for cleaning.

 

thanks guys. both posts helpful

I read that too about only the water evaporate....but you know...my NOSE tells me otherwise since "sometimes" I can smell a faint rotten egg smell and it's not coming from me I promise....but the battery. So I'm just curious.

I have a feeling it won't help as you suggest.

This batteries already toast.....nothing to lose except a few cc's of H2SO4

As you can see from the data and graph above, this battery is down to 1Ah or slightly less. So any change (or not) will be easily detected.

Even with that 1Ah, I'll bet the astronauts on Apollo13 would have given a kidney EACH to have had this battery with them on the way home

 

According to an article I read by Exide who are a major battery manufacturer, only the H2O evaporates, leaving acid in the battery and you should never add additional acid as it eats away the structure if its too strong. May be worth looking up evaporation of H2SO4 and see what you can find out.
(also known as oil of vitriol) I think it readily absorbs moisture in the air.

Interesting question.....I found this....
https://www.cheresources.com/invision/topic/712-sulfuric-acid-evaporation-rate/
Partial pressure of H2SO4 = 0.21 x 10-7 bar
Partial pressure of water vapor = 0.12 x 10-4 bar
Total vapor pressure = sum of the above partial vapor pressures

Meaning evaporation is very, very low. But that is not considering heat or time.

In a sulfated battery, the H2SO4 is mostly in the form of lead sulfate and stuck to the plates in which case the Sulfuric acid is not likely to evaporate much more if at all.

https://en.wikipedia.org/wiki/Lead–acid_battery
Lead and lead dioxide, the active materials on the battery's plates, react with sulfuricacid in the electrolyte to form lead sulfate. The lead sulfate first forms in a finely divided, amorphous state, and easily reverts to lead, lead dioxide and sulfuric acid when the battery recharges.

So in a fully charged state or any state when liquid H2SO4 is present, I guess the question becomes do the Sulfur ions evaporate or is it that only the H2O is liberated and evaporates leaving all the sulfur behind?

 

Hello,

I found this about distalled water:

Why Use Distilled Water


Many mechanics and car owners use tap water to top off the battery. This can lower performance and shorten battery life due to water impurities that upset the normal battery function. Battery manufacturers recommend distilled water for better performance and longer battery life. Distilled water is water from which salts and minerals have been removed. Water from faucets, lakes and wells usually has dissolved minerals and salts. These minerals and salts affect the chemical action in the battery. The battery works harder to maintain its charge and does not operate as efficiently. When the battery works harder, its internal temperature may get hotter while the battery is working. This causes more evaporation and requires more water. Distilled water ensures the correct battery chemical properties are maintained.

This comes from this eHow page:
http://www.ehow.com/how-does_4901867_do-need-distilled-water-battery.html

Bertus

 

In a sulfated battery, the H2SO4 is mostly in the form of lead sulfate and stuck to the plates in which case the Sulfuric acid is not likely to evaporate much more if at all.

Bingo! All things being equal as exposed surfaces from low water inside the battery hard sulfate the acid concentration might be fairly normal but low in the remaining electrolyte until you refill that battery with pure water to normal levels. The 'acid' trapped in the hard sulfate won't be released during a charge cycle so the acid stays diluted.

 

So after a short charge of a couple hours I only got .774Ah

Still declining.

I'm going to charge the battery overnight and do another reading in the morning after a full nights charge....but it doesn't look good.
The next step will be to open the battery, surface scrape the plates, flush the battery clean, refill with acid and try again.

 

Caution: I used to use R.O. water but no longer. The Membranes are getting worse and worse
as time goes along, Not unusual now days for stuff to get cheaper and cheaper.
the new membranes are measuring 60 to 200 used to be 20 to 30 new.

I use distilled now and It always measures about 1or2 on my tds meter.
get it from several places Wally, FrysGrocery, SaveWayGrocery, never got any bad so far.
.

 

I read that too about only the water evaporate....but you know...my NOSE tells me otherwise since "sometimes" I can smell a faint rotten egg smell.

That rotten egg smell is typically Hydrogen Sulphide gas. Could it be that some dissolved impurities in the 'distilled water' liberated H2S? Why not measure the specific gravity of the liquid? I am no expert, but battery charging services here measure the specific gravity of each cell, and am told that needs to be within a pretty tight tolerance.