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How does Sulfation Drain a Battery?

By R. Kayne
Updated May 23, 2024
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Due to chemical interactions inside a lead battery it must be used on a regular basis or sulfation will occur. Sulfation interferes with the ability of the battery to accept, hold and deliver a charge, and left unchecked will render the battery useless far short of its designed life. In understanding how, and under what circumstances sulfation takes place, one can take measures to avoid it and prolong battery life by years. This is not only good for the pocketbook, but for the environment.

In basic terms, a common acid battery consists of a series of oppositely charged lead and lead oxide plates which divide cells. Battery cells are filled with a mixture of 65% distilled water and 35% sulfuric acid, or electrolyte solution. Electrolyte produces electrons. While under charge electrons move between the plates discharging energy in the form of volts. The lead plates convert this energy into electricity. Each cell can produce about 2.1 volts of charge, therefore a 12.6-volt battery, for example, requires six cells.

Sulfation occurs when the battery sits for long periods of time and the electrolyte solution begins to break down. Sulfur in the solution leaches from the electrolyte, sticking to the lead plates as converted lead sulfuric crystals. These crystals coat the plates preventing them from doing their job at the next crank. Compounding the problem, the electrolyte solution becomes weaker because it is lacking the sulfuric acid that has converted to crystals. This equation reduces the ability of the battery to deliver and accept a charge.

Stages of sulfation include an initial form that might reduce quick starting, but will be absorbed back into the electrolyte when charged. With more time, stage one progresses into stage two sulfation, wherein small crystals begin to form on the plates. At this point the battery might not start the vehicle, and will require a greater charge to break the crystals free. If the battery sits long enough, stage two sulfation will advance into stage three, resulting in a non-chargeable battery. The lead sulfuric crystals of stage three sulfation can grow so large as to cause the battery case to bow.

To keep sulfation from occurring, a battery need only be maintained in a fully charged state. For those vehicles and crafts used on a daily or semi-daily basis, this isn’t a problem. However, pleasure boats, personal aircraft, recreational vehicles, off-road vehicles, and motorcycles that are used occasionally will develop battery sulfation, barring preventative measures.

To slow this process, some people disconnect the battery from the vehicle when not in use, but sulfation and self-discharge still occur. A better, more convenient and effective solution is to use a device called a battery conditioner. A battery conditioner will keep the battery fully charged between uses, without overcharging it. Battery Minder and Battery Tender are examples of two such products, designed specifically to prevent sulfation and extend battery life by as much as several years.

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Discussion Comments
By anon269756 — On May 19, 2012

I my humble opinion, sulphation does not drain a battery. It is the direct result of the creation of an electrical current. When the sulfuric acid molecules break apart from water (H20) and combines with the lead plates which are lead dioxide (PbO2) not lead oxide.

The result of this new combination is a change from lead dioxide to lead sulphate so a battery immediately becomes "sulphated" and recharging a battery reverses this process. The problem with the lead sulphate is extended time when it remains in that form as it continually hardens and becomes difficult and then impossible to remove which at first reduces the capacity of a battery and eventually leads to its complete failure.

A battery will drain through use (creating electricity) or self discharge at any ambient temperature of 38 degrees F or higher. The higher the temperature, the faster the self discharge. There are two ways to stop this natural occurrence. One is to store the fully charged battery at 38 degrees F or colder and it will maintain its full charge almost indefinitely or second, keep the battery at full charge with a charger that has a "Float or Maintenance" feature such as the BatteryMINDer.

By anon161013 — On Mar 17, 2011

@anon40834: If your batteries failed within six months this is a serious problem with either the batteries or your charging equipment, nothing to do with sulphation. They should also be covered under warranty.

By anon88831 — On Jun 07, 2010

thanks. very helpful.

By anon65265 — On Feb 12, 2010

@anon40834: Use two sets of batteries, charging one fully then switching them to discharge it while the other charges fully.

By anon47101 — On Oct 01, 2009

this article is very helpful. i'm a sixth grader and im trying to figure out which battery brand lasts the longest and how to take care of your batteries so this passage/article is very helpful. thanks for posting it on this website. thanks, Angel and Justice. :)

By anon40834 — On Aug 11, 2009

How can deep cycle lead acid batteries ever be kept to full charge if they are used in a solar panel charging system, whose charging current varies according to how bright the sun shines?

On dull days, the batteries won't receive adequate charging, yet still be expected to deliver current.

My deep cycle batteries failed within 6 months, due I believe, to sulphation caused by indequate availability of charging current.

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