Sometimes, terminals or posts of lead acid batteries corrode due to which connection between batteries and appliance cuts off completely or weakens. In vehicles, corrosion restricts ignition of engines because enough current is not drawn from batteries. What causes this corrosion, what compounds are formed on terminals, and how to prevent this corrosion from happening again, complete details are given below. Equations of chemical reactions are also mentioned to help understand the process of corrosion.
Causes And Compounds Formation:
In case of sealed lead acid battery (also known as SLA battery or dry battery), corrosion happens when electrolyte makes its way out to battery terminals through any leaks or joints. In case of flooded lead acid batteries (wet batteries), electrolyte can jump out while carelessly pouring water into cells. Also, fumes of sulphuric acid which is a part of electrolyte and actually responsible for corrosion keeps arising out of vents of flooded lead acid batteries when battery is charging or hot. Overcharging heats up the battery and heat increases the volume of electrolyte filled inside it. This electrolyte can leak out of vents of overcharged flooded lead acid battery if it is topped up with too much water and also SLA batteries through loose joints.Posts of lead acid batteries are mostly made from lead. Lead itself is a stable metal. Its reaction with sulphuric acid is very slow. If contact happens at battery posts, the compound which is formed as a result of reaction is lead sulphate ( PbSO4 ). The chemical reaction between lead and sulphuric acid is accordingly:
Pb (s) + H2SO4 (aq) → PbSO4 (aq) + H2 (g)
Sometimes, it also happens that copper clamps or ringed copper terminals which are used to connect battery with wires corrode. Copper itself is not reactive even if dilute sulphuric acid is poured on it. But when electricity passes, it reacts with sulphuric acid and produce copper sulphate ( CuSO4 ) along with water and sulphur dioxide gas. The equation of this chemical reaction is following:
Cu (s) + 2 H2SO4 (ℓ) → CuSO4 (aq) + 2 H2O (ℓ) + SO2 (g)
The white substance which you see around battery terminals is either lead sulphate made from the reaction explained one paragraph above or anhydrous copper sulphate made from the reaction explained in above paragraph. Anhydrous copper sulphate changes to blue colour when water is added to it. The bluish substance which you see around corroded copper terminals or copper clamps is hydrated copper sulphate.
Cleaning Corroded Battery Terminals:
To clean lead sulphate or copper sulphate from terminals, first disconnect terminals from battery. Make sure, you are wearing gloves as these chemicals can affect the skin. Now, wash terminals with clean water. If rust washes away, then no more hassles. Otherwise, wash them with the solution of any of these bases caustic soda, washing soda or baking soda made by dissolving base into water. Simply dipping battery terminals or clamps for few minutes into solutions of these bases also works. After cleaning with base solution, wash terminals again with clean water to clear away the remnants of base.
It is advised not to pour the solution of any of these bases over battery posts to clean them as it might gain access to battery interiors through vents, joints or leaks. If entered, it can badly affect the performance of battery. Instead, use a cloth dipped in base solution to clean them or use a brush to rub the rust off. Take extra precautions while cleaning hydrated copper sulphate which is bluish in colour because it is poisonous.
Prepared solutions are also available in markets to clean the corrosion. You can also use them.
Prevention from Corrosion:
1- Corrosion can occur in dry environment but it is boosted by moisture and salts present in water. Therefore, keep the batteries away from moisture and damp places.
2- Do not wash interior of car engine bay with water. Water increases speed of rusting metallic parts of engine bay which are not covered with paint and also joints of power cables and battery terminals.
3- Always keep the battery top dry and free from dust and other pollutants. After pouring water into flooded lead acid battery, never forget to dry the surface of battery. Close the caps of individual cells tightly.
4- Apply Petroleum jelly or grease to battery terminals to protect them from corrosion.
5- Use clamps and battery terminals made from good quality copper which are also alloy plated. Layer of alloy prevents terminals from corroding.
Batteries in Series and Parallel Connections (Battery Packs)
Can you use de-ionized water in place of distilled water when topping up the fluid level in a car battery?
Yes you can use deionized water in place of distilled water.
Basic chemistry says the cause of corrosion is the electric field due to a voltage drop. The electric field causes a current to flow if there is a conductor like electrolyte. The current carries electric charges and those charges cause the corrosion.
A voltage drop can happen when there is a loose connection or corrosion on the battery terminals. The resistance can cause a field strength of several volts per millimeter and the corrosion is very high. Be sure the terminals are clean without resistance between the battery and the terminal so there is no electric field to cause the corrosion. Be sure the battery is clean so there is no electrolyte between the + and – or between the battery and the car body or frame so the high resistance does not allow the current to flow in the field between the terminals so the corrosion is again prevented.
Thanks God found a complete solution to my problem…..my oral pass
EVERY vehicle my wife owns get the white corrosion. (Cavalier, Eagle Talon, 2 Plymouth vans, & even 2015 Ford Edge) I have gotten very minor issues of corrosion. Specifically, I bought the Cavalier from her & in 3 years never got the full Santa’s beard to show on terminals every few months (like it was when I got it from her).
Also, no vehicle I’ve ever owned had this much of an issue.
So, I’m confused as to why it happens to her, which gives ME the pleasure of cleaning.
Thank you for any ideas & this very informative read.
Thank you, my cleaning made easy.
Hey Talal. Nice article. I think whether electrons flow in a conductor from positive to negative or negative to positive is still a Theory. But yes they flow.
I have battery discoloration (change to black color) in terminal +ve, whats the cause and how to prevent it? what is the difference between petroleum jelly and oil on protecting terminal?
Lead has oxidized on terminal forming that black substance. Clean it with cloth or brush.
Petroleum jelly is viscous. It will stay at place. Oil won’t.
Hi there I drive a 2006 vw golf 2litre Fsi….For bout a few mnths now ive been batteling with a battery issue…..bought a new battery in december last year, problem started before I bought the new battery…….sulphur build up which causes power loss to vehicle or battery and I cannot start my car, I have to remove the positive terminal, tap it until I get a spark and only then my car starts, I went as far as cleaning all the white build up & replacing the positive terminal & cable…..it worked for 2 days only
You must lubricate the terminals.
Ok here is a little different issue and on a motorcycle not a car I had a couple days ago. The ends of my plug wires connected to my plugs were corroded kinda of a white colored powdery like some of what has been described. Plugs are about 45 days old and have very very few miles on them, wires are a year old. The bike runs on a Morris Magneto and no battery at all. What caused this? Ive never had this before.
Does rusting cause leakage under vehicle? my drive is rusted due to acid leakage but have been unable to identify until today. Does anyone know how I could get drive cleaned from the the rusting?
only use petroleum jelly after attaching cables to posts. connection should be metal to metal.
I own a 2007 Lexus Gs350 with 124,000 miles. Mechanic noticed corrosion on battery so he cleaned it this was three days ago. Checked battery today and it is full of corrosion again. Why is this happening?
Check if battery is getting over charged (indication: hot battery). Faulty alternator will keep charging the battery even if it is already full. Also if your car battery is quite old, replace that.
Note: Placed my incorrect info note in reply instead of comment section. My note should have said air bag recall and “not” battery recall. My error.
Note: “Recall was on air bags—-Not on Battery. My error.
Does battery corrosion turn to rust on nuts and screw on connections? Have auto w/40,000 miles (Toyota Avalon)? Dealership was to install filter, etc. on battery recall, destroyed carpet, messed up AC & when I chkd under hood, battery had rust on nuts, connector arm on battery & rusted battery encasement. Tried to claim carpet had dry rotted when in fact mechanic cut carpet to remove.
Yes. Corrosion leads to rusting of parts.
hello Mr. Talal,
Curious to know where you found information or a study that shows petroleum jelly works over time to prevent corrosion
Just apply the petroleum jelly on corroding part and see if it works or not. You only need the “common sense” and not the research papers.
Copper sulfate forms on the positive terminal because the negatively charged SO4 ions are attracted by the positive charge.
Speaking from experience . I was a motor mechanic
Most of my life. Anything like the corrosion on old
Positive earth cars was very bad sometimes going
Down all the way to the car body. Didn’t happen on
Negative cars to any great extent. I am convinced it was
Caused by the incompatibility to our planets negative
Polarity in the northern hemisphere . A sort of electrical
ions not matching up. Could be wrong here but that’s my theory. Since most cars are made in the northern
Hemisphere the negative earth system has won out.
When car body was made to supply current, current flowed from positive body to negative battery terminal and alternator. Water can stimulate corrosion. So when electricity passed from body, body started corroding more. That was a total stupidity to use car body to supply current. It was not safe at all. But you know people learn from their mistakes. Also note that it was thought back then that current flow from negative to positive. But later it was discovered that it flows in opposite direction. So they fixed the mistake. That’s my opinion.
You might be convinced, but unfortunately whatever evidence you experienced to make that case was somehow compromised. There is no Northern Hemisphere, Southern Hemisphere phenomenon which would affect the preference for positive or negative ground electrical wiring. On the other hand, your observations about how some early model cars used positive ground is correct. Indeed lots of British cars, in particular, had positive grounds. However, the availability of advanced electronic devices (transistor radios, electronic ignitions, even diodes used to protect the contacts in electric fuel pumps) provided market incentives for standardization of the negative ground systems. Those market incentives, and availability of improved wiring insulation sealed the deal, so today virtually all automobiles use negative ground wiring.
Years ago battery terminals corroded on British and
American Ford cars. This was because the earth terminal was positive. Our planet earth is negative
Polarity in the northern hemisphere and positive polarity in the Southern Hemisphere . That’s why all
European cars have negative earths now. Was this helpful to you all.
What kind of sorcery is that? Cars all around the world have got negative body (ground) and positive supply through wires. That’s for safety. Also supply of current via copper wires which is an excellent conductor will result in trouble free running car. This can never be achieved by making the body a source of current.
Sorcery is the use of magic – and this has nothing to do with magic.
Yes, cars all around the world use their bodies (if they’re metal) as a negative ground for their electrical system. I knew someone with a ’62 Jag that had a positive ground system – many British cars through the 60s had a positive ground.
Use of copper wires does not “result in trouble free running car.” There are many things that can go wrong with a car that have nothing to do with how it’s wired. As long as the wiring is all proper and connections are good, the electrical system will work as it should whether it’s a positive or negatively grounded system. There is no point of safety here. One system is no safer than the other.
By the way, the battery and alternator are the source of current for a car – not the car body.
Many cars through the ’60s had positive grounded systems, mostly British cars. One of the reasons for this was that before the ’60s the insulation of wires was very poor, and would crack and sometimes desegregate in areas of stress with time. This caused wires with originally somewhat poor dielectric strength to worsen with age. Where the insulation was compromised, corrosion would form. If it was a positively grounded system, there was reduced corrosion, and with the often damp climate in England, they opted for the least corrosive electrical system.
With the invention of quality plastic insulation, they slowly moved to negatively grounded systems, mostly to keep pace with modern electronics, which at the time meant electronic ignition systems and transistor radios.
(Note: Dielectric Strength is a measure of the electrical strength of a material as an insulator. Dielectric strength is defined as the maximum voltage required to produce a dielectric breakdown through the material and is expressed as Volts per unit thickness.)
Northern hemisphere and positive polarity in the Southern hemisphere makes no difference.
what is the reasons for electrolyte leakage at +ve pole in GEL tubular cells (fresh product, just installed)
does it manufacturing defect? bad storage? bad handle at installation? bad commissioning and charging?
Probably manufacturing defect.
Excellent article, very well written. I believe the corroded terminals were impacting the alternator being able to charge battery properly, so I will be replacing them. The alternator tested good. Next step will be to replace serpentine belt for good measure. I appreciate what you wrote about what to avoid as much as what to do, and why. I hope I can find other articles you have written, I like your style, backed up by knowledge.
For once a explanation that I can understand. My wife’s car had corrosion on the battery terminals. I read the directions to her step by step and then we got to the step that said do not pour water n soda directly on to the battery post. Since this was after the step on what to use we were not aware to not pour it on. Can u please make a note in parenthesis in the step on what to use saying (do not pour soulutions directly on the battery posts). So that ppl don’t do what we did. Otherwise great information!
Thanks Talal for that wonderful explanation.
Please why does it only occur on the positive terminal of the battery? What is that blue corrosion called? What effect does that corrosion have on the performance of the battery?
I have a ’01 Honda Odyssey. The + battery terminal is (was) made of stamped metal and has corroded /disintegrated to the point where it could no longer be tightened on the battery terminal. When I removed it off I could easily see that is was almost split through.
The battery has three cables going to the terminal. One large (maybe 3 AWG) going to the starter motor I think, another the same size going to a large fusebox and another smaller wire to a small fusebox next to the battery.
My mechanic cut off the old terminal and replaced it with one that has a large stud and a wing nut on it. He then crimped ring terminals onto the three cables and fastened them to the stud on the new terminal.
My question is: He did a lousy job of crimping one of the large cables into the ring terminal, and it is loose where it is crimped. The cable did not fit into the terminal, and there are 4 or 5 strands NOT crimped in it. The cable is loose in the terminal – I think probably less than half of the strands are really crimped in it.
I want to change the terminal, and have a copper ring terminal that looks like it would fit, and I can solder it after crimping it – but have read that copper reacts with either the hydrogen gas the battery out gasses or the sulfuric acid in the battery and will damage the terminal.
Is this so? Will I be ok using a copper terminal?
Use copper terminal. Apply grease or petroleum jelly to protect that from corroding.
03 kia sedona, brand new battery, alternator has been checked, both are working good. Parking brake light and battery light turned on together. Had mechanic check it out he said was bad connection due to corrosion of terminals cleaned it and problem went away…….month later same problem again killed my new battery replaced it and still showing parking brake and battery light. Am I missing something? What step should I take now, reading about ground cable to alternator may be the culprit. Anyone have any clue if it sound right?
There could be some problem in wiring…
No tip, but a question. White ash was all over the battery, but the terminals were fine! Brushed the ash off, but don t know what caused it. Any thoughts? As I said, the terminals were clean.
Where was this battery placed?
I have a similar issue. My car is not used often so I disconnect the positive lead from the battery. I now have a lot of the white corrosion under the battery, none on the terminals. Thoughts
Leaking electrolyte is causing that at the bottom of battery. Leakage could be from top of battery, joints or vents.
Thanks Talal, I will clean it, grease the terminals and reconnect the leads
It is either the starter or the battery. In most cases I would say it is the battery since it does start with a boost. You can check for battery positive at the starter the next time it won’t start to rule out a bad starter.
i have the same problem with my keyboard. I made a solution using baking powder and applied it on one terminal. But since the other terminal is deep inside, i couldn’t see it. So i poured a small amount into it.
but now when i put new batteries in it, it doesnt work….
May be liquid has damage it. You should not have poured it.
Thanks Talal for a great and informative article. Also, thanks everyone for your questions and comments. I’ve had this problem on a Mitsubishi Endeavor for 5 years, and I’m on my way outside now to clean it this year. This really helped me understand why, and what to look for in the future.
We have heard of a trick of using pennies placed on top of the battery, one held in place with a drop of oil near each post. The copper supposedly draws corrosion off the battery terminals. We don’t know whether this works or not – if you know, please let your fellow readers know using the comments at the bottom of this page.
My wife’s 2012 Taurus has been through 4 batteries due to corrosion of the terminal. Ford is giving her the run around. Why is this happening?
Make sure that car alternator (generator) is working fine. If it is not cutting off charging, that will not only result in excessive heating of battery but electrolyte might also seep out of battery and cause corrosion of its terminals.
Change the battery brand as well. Try something new and reliable.
Do batteries have a tendency to corrode more prolifically as they become older? Is it best to use a brass wire brush to clean off corrosion, rather than ordinary steel wire? I have been advised that using a brass wire brush will not create sparks whilst cleaning the battery posts, thereby eliminating a potential source of igniting the hydrogen gas produced by the battery.
Use plastic brush dipped in base solution. Pour a little on terminal but make sure it does not spill away. Besides you can use brass wire brush.
If terminals are too much corroded, change them instead of cleaning them.
The battery on my car is only a year old . It wouldn’t start so I took a look and the positive terminal was heavily corroded . Could this be a bad battery ?
Clean the terminal and you can continue using battery. Look for any leakage.
One thing to add, when you pull the cable off the battery and have done the cleaning with baking soda solution, you then need to brush the battery post as well as the inside of the cable clamp until they are shiny. You can buy a cheap brush at Wal-mart that is just for this purpose or use sandpaper.
Charles H. Young III
I service home/business alarm systems that use a sealed lead acid battery for back-up voltage when the power goes out. I have ran across where the battery leads/wire have broke due to corrosion. I alway thought it was due to a poor connection over a long time and after replacing the terminals and battery I would apply dielectric grease. However tonite I had this issue on a system that was less than 2 years old. I also found leaking battery acid on the outside of the battery. If I understand your article the leaking acid was the catalyst that caused the corrision. The bigger the leak the faster the corrision happens. Did I understand you correctly?
It is the electrolyte (battery acid) that seeps out of battery joints or cracks and cause corrosion. (not catalyst. Catalyst is a different thing) Some manufacturers are too dumb to properly seal the battery. Thus electrolyte keeps evaporating or leaking and cause corrosion of terminals.
Thanks for your good article
but why this process occur in only one terminal of two positive terminals?
Corrosion can occur on any terminal if battery acid makes it way to it.
Battery terminals properly cleaned and kept on shelf become black before sale/installation on vehicle. What could be the reason?
Corrosion. Clean them again before fitting.
Thank you for your very good explanation, Talal. I have been told by a mechanic that petroleum jelly/grease doesn’t do anything to prevent the corrosion problem. Are you able to give a more detailed response to explain why you believe jelly/grease helps?
Try it yourself. This is a standard practice to grease terminals to protect them from corrosion.
Strongly disagree. Here’s why. Petroleum Jelly is not electrically conductive but rather an insulator. That, meaning if any gets on the battery clamps or posts you’ll lose most or nearly all flow of current. If anything is used it must be a conductive jelly or paste. It’s best to use the manufactured products specially made for this purpose. Home remedy’s aren’t always best and in some cases can cause disastrous results.
If battery clamps or terminals are tightly held, there is no way petroleum jelly or grease or anything else would stop the flow of current.
Upadated the post. Originally posted on May 09, 2013.
My inverter battery 100 AH , Once due to overload low battery alarm came .After that even after full charge back up time is very low.Any solution for this
Seems like inverter problem.
Saurabh Kumar Singh
In this case your battery goes in deep discharge so your battery back-up goes down.
So unplug your battery from Inverter and fully charge the battery through external charger.
If the battery gravity shows fully charged (1250) connect it again to Inverter.
I think your problems will be solved after this.
Very informative article, good job Talal.
Thanks god, found a complete solution to my problem. My car battery terminals were covered with whitish substance. Cleaned them with soda solution and applied gel.
Very well explained how to clean and prevent corroded battery terminals from further corroding.
Even though I am using gel batteries as well but they also have got the issue of corrosion build up at terminals.
Battery acid can leak from joints or vent causing corrosion. Humidity in air or water can stimulate rusting process of terminals.
Great article with detailed explanation! My battery terminal was corroded quit badly and the corrosion deposit expanded and made the copper clamp was so tight that I could not turn it. After watched with the soda solution, and eventually able to turn it with a plier. Dipped the clump into sofa solution, and then dried up everything and put some grease on it. Cleaned up the terminal cover and put it back on.