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Electronics => Repair => Topic started by: @rt on May 09, 2019, 02:35:42 pm

Title: Corroded Batteries (suspect issues)
Post by: @rt on May 09, 2019, 02:35:42 pm
Hi :)
There are a lot of posts here about things with corroded batteries.
I don’t have a lot of experience with that specifically, but something of mine did drop continuity with one of the AA terminals in the battery holder after a leak.

My question is very general. Is it most often a ruined PCB trace or discontinuity across a connector pin that is first to go wrong?
Is it often ruining components too, by eating away chip legs entirely?
Cheers, B.

Title: Re: Corroded Batteries (suspect issues)
Post by: bob91343 on May 09, 2019, 02:56:04 pm
It's just corrosion.  When a cell leaks, the corrosive fluid gets in places where it causes metal to oxidize and lose its conductivity.  A barrier is formed which must be cleaned away to restore operation.

This chemical action occurs nearly everywhere it touches.  Copper is very vulnerable, turning into oxide and sulfate, both of which are insulators.  This can be on circuit traces, connector pins, and wiring.

In addition, there can be leakage paths created that will cause currents to flow where they can cause trouble.

So the short answer is, clean everything and inspect closely to see what damage has occurred.  Repair damage.

It's been suggested to spread the area with baking soda to neutralize acids.  I think that makes a bigger mess, but that's just me.  I prefer washing the areas, maybe some water or solvent.  Polish damaged surfaces.

I am unsure whether this answers your question.  My experience is that connectors are the first to go, but if left uncorrected for a long period, anything will corrode.
Title: Re: Corroded Batteries (suspect issues)
Post by: @rt on May 09, 2019, 03:03:10 pm
That pretty much answers it. Thanks :)
Title: Re: Corroded Batteries (suspect issues)
Post by: Ian.M on May 09, 2019, 03:45:12 pm
Most battery electrolytes that are likely to leak are alkaline (exception: Lead Acid batteries) so 'neutralising' with baking soda (sodium bicarbonate) which is also alkaline is pointless.   If you use white/distilled vinegar it will actually neutralise the alkaline corrosion, and make the metal salts residue soluble in water, but you then need to rinse three times to be certain you haven't left any traces of acid from the vinegar.  Use distilled/deionised water for the final water rinse then shake and blot off as much water as possible and spray the board down with IPA to remove as much water as possible and form an azeotrope with the rest and dry in a warm place.

If the electrolyte bridges two or more tracks pads or pins at different voltages, the more positive one will usually be preferentially eroded.  With several volts difference, a track, pad or thin pin can be totally eroded away in minutes.
Title: Re: Corroded Batteries (suspect issues)
Post by: @rt on May 10, 2019, 04:25:17 pm
Hi Ian,
On a Commodore Amiga forum, where the RTC batteries leak, and ruin some bus bits so RAM goes silly,
the question was asked why some people use lemon juice, and some bicarb of soda, and it was explained that the bicarb has pH 8.5 which is closer to neutral,
and then rinse with demineralised water or whatever. That was the explanation given anyway.

I can’t really have an opinion on it. I’ve chased good boards and tossed the batteries, and I don’t care about an RTC in a vintage computer to even replace with something else.