Accelerated Corrosion in Car Batteries

Question

I am trying to get a better understanding as to what can cause a car battery to corrode at an accelerated rate.

My friend's truck has developed an electrical issue and we noticed that the terminals on the batteries corroded about 2 days after cleaning them. The batteries are fairly new. The truck has two batteries and we noticed that one battery has the negative terminal corroded and the other has the positive terminal corroded.

Is there a specific reason why they would corrode in such a short amount of time? Is there a difference as to why the negative terminal corrodes versus the positive terminal?

Thank you.

Answer 1

When a truck battery, most probably 2 open type lead acid batteries,is at the end of it's charging cycle. Meaning completely charged to 2x 14,4 volt then the batterie start to boil thereby relasing water and with that sulphuric acid.

This might be the reason of the corrosion here.

Furthermore only cleaning is not enough. After cleaning the battery poles must be protected with something like vasiline to eliminate the risk that the sulphuric acid vapor can reach the poles. Make sure the poles are in good order and well attached to the poles. Normally the battery poles and connectors are made of lead. If different you are also in for corrosion problems.

Corrosion can also come from a galvanic path between the body of the truck and the poles. This has also to be kept clean. If the old battery has been boiling over due to a faulty alternator regulator the bottom of the housing should also be checked and cleaned if required.

So there are some tasks to be done.

1. Clean the battery poles and protect them
2. Clean the battery housing and maybe place an isolator underneath the batteries.
3. Verify if the alternator indeed supplies a max of 28.8V and not more

Note: If the batteries are 2 x 6 V making 12 V then the above is only 14.4 V

Answer 2

This sounds like galvanic corrosion: metal parts connected to positive potential start to repel positive ions they are made of. The presence of electrolyte (usually moisture) opens a path to those ions, so they migrate away from the metal eroding it.

Depending on how much moisture there is, and how the contact between battery terminals and the clips connected to them looks like, several scenarios are possible:

1. Good contact: the positive terminal and the clip have essentially the same potential. They corrode together, provided there is a path through the moisture to the negative battery terminal. Note that if there are several batteries in series, negative terminals of some batteries can still be at a positive potential to the metal frame, so they will corrode just as well. Since the path to the negative terminal is relatively long, this kind of corrosion happens slowly, unless you submerge your truck in water.

2. Bad contact: the clip is at lower potential than the positive terminal, and very little moisture is needed to provide a path between them, so corrosion happens very quickly. A similar process happens at the negative terminal, in that case the clip will corrode rather than the terminal. You might want to double-check what exactly is damaged.

3. Different materials used for battery terminal and the clip. The terminal and the clip make an electro-chemical cell of their own, and corrosion happens without involving the battery itself. This should not happen to you if you use correct batteries and original wiring.