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I put a new battery in my car about 8 months ago. After a problem starting a couple days ago, I found that there was massive corrosion under the battery terminals, so I cleaned them out and reconnected.

I've never had this problem with this car (which I've owned over 10 years) with any previous battery (nor in any other car ever). My use case hasn't changed any. The battery is showing good charge. The charging system is operating properly.

What can I change to avoid a recurrence?

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6 Answers 6

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Corrosion on the terminals is due to hydrogen gas being released from the acid in the battery. It mixes with other things in the atmosphere under the hood and produces the corrosion you see on the terminals. Generally, if the corrosion is occurring on the negative terminal, your system is probably undercharging. If on the positive side, it is probably overcharging. Most often it will be seen on the negative side because the battery is usually in an undercharged situation. This is just the nature of the beast, I'm afraid.

You will need to thoroughly clean the corrosion from off the posts. You can use baking soda and water solution to help in this endeavor. Ensure you have eye protection, clothes which you don't care if it possibly gets ruined (acid can do nasty things), and some type of gloves (nitrile gloves work great). Clean the area using the solution and a brush. It doesn't have to be a steel bristle one, just one which is stiff enough to remove the gunk. You will have to remove the battery cables to get them completely clean (sorry about the radio channel presets!). Finish your clean up with a good dose of water to flush the area of any residual corrosion. If you don't, it can eat away the paint in the nearby areas.

When done cleaning, to help slow down the corrosion process, coat the terminals with grease (high pressure grease or wheel bearing grease works as good as anything). It doesn't have to be a lot, but ensure total coverage of the metal at the terminals. Cover the outside of the terminals after you have put the cables back onto your battery. You can also purchase a aerosol spray coating which you can purchase from your local parts store. Your main objective is to keep the lead, escaped hydrogen gas, and oxygen from mixing which forms the corrosion you see after a period of time. Over time the grease will break down and corrosion may start, so regular cleaning and reapplication is a must. If you do this about every six months, you should be in good shape.

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    Could the under/over charging be a symptom of a bigger problem (dying alternator, faulty connections not carrying enough current)? Would you suggest digging deeper to diagnose the underlying problem before fixing the corrosion? Won't it just come right back?
    – Eric Seastrand
    Commented Aug 4, 2015 at 16:09
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    @Eric - You should ask this as it's own question and refer back to this one to help you explain. As it stands, it isn't what the OP was asking for, considering they stated "the charging system is system is operating properly" ... Also remember, I stated generally this is how it is. Corrosion occurs if the terminals are not protected. Having the over/under charge state will just emphasize it.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Aug 4, 2015 at 16:19
  • One trick I learned in auto shop class (besides coating the terminals after the cleaning) is to put a copper penny near each terminal; the corrosive elements will attack the penny instead of the terminals.
    – Mark Stewart
    Commented May 18, 2016 at 19:16
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    @AdamPlocher - I appreciate your input. While the question is related, it wasn't even asked by the OP. We should not be in a habit of using the comments to answer questions. The idea of Stack Exchange is to ask/answer questions so people can find the information. Answering a comment with another comment buries the information. Answering a question brings it out into the light where it can be found.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Jul 12, 2018 at 13:13
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    @AdamPlocher To add to Pᴀᴜʟsᴛᴇʀ2's comment, if the question does indeed get asked elsewhere, it's trivial to add a link to it in the comments here at that time.
    – Dan Henderson
    Commented Sep 19, 2018 at 14:53
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Much of the corrosion is due to bimetal contact between copper and lead alloys. Nothing to do with Hydrogen.

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    Agreed. Hydrogen is broken off of H2O during the charging process. Has nothing to do with the buildup of corrosion on the terminals.
    – DucatiKiller
    Commented Oct 9, 2015 at 17:35
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While the battery does produce hydrogen gas The corrosion is probably due to lead sulfate. The metals on the terminal post and connecting fitting are to close (by design) in galvanic similarities to be an issue.

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    And what causes the lead sulfate?
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Dec 31, 2015 at 2:45
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After some significant testing I now have a better solution than what I originally accepted. Use the auto store battery felt pads along with the grease for a long-term, lasting solution.

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  • Do these battery pads actually work? I posted a question here to ask - mechanics.stackexchange.com/questions/87500/…
    – culix
    Commented Jan 2, 2022 at 23:25
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    @culix The pads definitely work. I had a battery that continually formed corrosion. Grease helped some but wouldn't last. Finally gave in and put the pads in, problem solved.
    – Brian Knoblauch
    Commented Jan 4, 2022 at 11:40
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If grease can be used in battery terminal , why a petroleum jelly is supplied with battery and as per technical installation, supplier directs to use petroleum jelly not a grease. please need help on it.

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    The supplier providing petroleum jelly with the battery is the manufacturer thinking ahead so the customer does not have to buy grease when they purchase the battery. It does not mean that grease cannot be used. IMO, I wouldn't use grease or petroleum jelly. It's a moot point.
    – DucatiKiller
    Commented Jan 12, 2016 at 4:31
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I encourage car owners no to apply grease on car battery terminals rather to apply petroleum jelly

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    Please elaborate. What's the advantage of petroleum jelly?
    – Brian Knoblauch
    Commented Oct 22, 2015 at 11:18
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    I think this could be edited into an answer, let's let it stand for a bit.
    – Brian Knoblauch
    Commented Oct 23, 2015 at 12:03
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    @BrianKnoblauch - While I agree there could be an answer if fleshed out, there's no real reason to use petroleum jelly over grease. Either one will protect the posts, but grease will stay longer than petroleum jelly due to the melting point of the product. The main purpose of either is to keep the gasses away from the lead of the posts & terminals. Grease is going to do it better for longer.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Oct 23, 2015 at 13:04

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