What is battery acid

Battery electrolyte is the liquid substance that's found in most car batteries. It's sometimes referred to as battery acid, because it's highly acidic. In fact, battery electrolyte is actually made up of a mixture of water and sulfuric acid.

When the electrolyte level in your batteries gets low, you may find yourself wondering what you can use to top it off. And if you remember the science courses you took in high school or college, you may find yourself wondering exactly what kind of electrolyte to use.

For instance, could you fill your battery with Gatorade, salt water, baking soda, or some other kind of electrolyte, in an emergency situation, to keep it from going dead?

The answer is no. Never put any kind of electrolyte in a lead acid car battery.

Although Gatorade contains electrolytes, salt water can act as an electrolyte, and baking soda, or sodium bicarbonate, can break down into electrolytes, you should never put any of these things in a battery.

If your battery electrolyte is low, the only thing you should ever add is straight water. There are some very specific circumstances where sulfuric acid can be added, such as if the battery tipped over and leaked, but never, ever add anything else.

What Does it Mean When Battery Electrolyte is Low?

When your mechanic, or a friend who knows a lot about cars, tells you that your electrolyte is low, they mean that the fluid level in one or more of the battery cells has dropped below the top of the lead plates.

Car batteries are composed of a series of lead plates submerged in a bath of water and sulfuric acid, which acts as an electrolyte, and it’s pretty important to make sure that the level never drops below the top of the plates.

If the electrolyte in a battery does drop below the top of the plates, and they are exposed to air, a chemical process called sulfation starts to take place. This process can drastically shorten the life of a battery, as it interferes with the normal operation of the cells, wherein the sulfuric acid in the electrolyte is absorbed into the lead plates as the battery discharges and then released back into the electrolyte when the battery is charged.

Adding the Right Kind of Electrolyte to a Battery

Gatorade might have the right kind of electrolytes to replenish your body after a workout, but it doesn’t have what batteries crave.

The electrolytes in Gatorade and other similar sports drinks are primarily sodium and potassium, with smaller amounts of magnesium, calcium, and chloride. The other substances you may think of when hearing the term electrolyte, like saltwater and baking soda, also contain the wrong kind of electrolytes.

In the case of saltwater, the electrolyte is sodium chloride. Baking soda, on the other hand, is made up of sodium bicarbonate.​

Adding anything but water to a battery can instantly damage it, but some substances are worse than others.

For instance, baking soda can act to neutralize the sulfuric acid present in battery electrolyte. In fact, a mixture or paste of baking soda and water is one of the best ways to clean corrosion from battery terminals and cables.

Another example of an acid reacting to a base in a similar method is the baking soda and vinegar volcano experiment. That absolutely is not something you want happening in your car battery.

How Can Water Be an Electrolyte?

You may remember from science class that water, by itself, isn’t an electrolyte, so adding water to battery electrolyte might seem like a bad idea.

At first glance, it seems like you would just water down the existing electrolyte. The water can only be an electrolyte in the first place when mixed with sulfuric acid, so it stands to reason that you would have to top off a battery with a mixture of sulfuric acid and water instead of straight water.

The reason that you can add straight water to a battery to top off low cells is that when a lead acid battery loses water, it doesn’t lose sulfuric acid. Water is naturally lost during the process of electrolysis, and it can also be lost due to evaporation—especially in hot weather—while the sulfuric acid content doesn’t go anywhere, or is lost at a much slower rate.

An easy way to understand how this works is to think about what happens when you boil a pot of salt water. The water evaporates, but the salt remains behind. If you add plain water to the pot, the salt mixes back in, and you have saltwater again.

The same thing happens when you add distilled water to a lead-acid battery.

The only exception is if the fluid is low due to the battery tipping over. When that happens, the entire solution of sulfuric acid and water is lost. In that case, you need to fill the empty cells with a dilute mixture of water and sulfuric acid.

Prolonging Car Battery Life By Filling Electrolyte

Although you can prolong the life of a lead acid battery by keeping it topped off, leaving it empty, or allowing the charge to drain too low, can cause irreparable harm.

Once a battery reaches a certain tipping point, there's no coming back. So if a battery dies, and it won't accept or hold a charge when you try to charge the battery, after first topping off the electrolyte, you're probably dealing with irreversible sulfation.

The best way to prevent this type of situation from happening is to keep the electrolyte topped off as part of a regular battery maintenance schedule.

That knowledge isn't a whole lot of use when a dead battery has already left you stranded in less than ideal conditions, but keeping on top of it can help you avoid the same fate again in the future.