Battery Acid: What It Is and How to Test It Safely

Acid is used in varying concentrations in acid based batteries. Typically, sulfuric acid is used as acid. Lead-acid batteries are most common acid batteries. Increased use of these batteries in EVs has brought them in limelight. Paired with increased demand, increased electrical loads in automobiles has urged manufacturers to develop better quality products which could satisfy stringent demands. Here, we will dive deep into various concepts related to battery acids. In this article, you will learn the protective measures while dealing with such batteries. Safe testing of battery acid is another important aspect for users, technicians, and transporting agencies which needs appropriate tools and adoption of right method. Tools used to test acid’s specific gravity (SG) are discussed briefly to give an idea.

Acid in Batteries:

Typically, Sulfuric acid (H₂SO₄ ) is used in batteries which is odorless and colorless strong acid. Mainly, it serves the purpose of electrolyte. Though, it is not the only electrolyte being used in batteries. Lead-acid batteries are most common types of batteries which use this acid, so we will be using lead acid battery as an example while explaining any concept.

You must also know that fully concentrated or pure acid is not used in batteries. Instead, it is diluted with distilled water to make it 30-50% sulfuric acid. For car batteries, it is 37% concentration of sulfuric acid.

Why is Acid Used in Batteries?

In lead-acid batteries, chemical reaction takes place between lead, lead dioxide, and sulfuric acid. Lead comes from spongy negative electrode, lead oxide from positive electrode, and sulfuric acid from diluted electrolyte. As a result of this chemical reaction, electrons are produced which flow through load or external circuit and power it up. If sulfuric acid would not be there, battery would not serve its purpose, because this diluted acid facilitates reversible reaction and helps maintain battery’s capacity and voltage. Going one step ahead, it takes part in chemical reaction not just helping reaction take place but becoming fundamental in electrochemical reaction. As mentioned above, sulfuric acid serves the purpose of electrolyte so it carries ions which flow between positive and negative electrodes maintaining charge neutrality.

Sulfuric acid is also used in battery manufacturing process for lead-acid batteries so it could activate lead elements in the battery to bring power effect.

How Does Acid Take Part in Chemical Reaction in a Battery?

Basic to complex level study of batteries demonstrates that battery acid plays fundamental role in functioning of battery. It acts as an active component during electrochemical reactions and doesn’t stay in cells as a passive component.

Sulfuric acid or electrolyte has two plates immersed into it. Positive plate is made of PbO₂ (lead dioxide) and negative plate is made of spongy Pb (lead). Reaction takes place between sulfuric acid, lead, and lead dioxide. Here, electrochemical reactions of a lead acid battery, during charging and discharging process, are mentioned.

Discharge Reactions:

• At the negative plate: Pb + SO₄²⁻ → PbSO₄ + 2e⁻
• At the positive plate: PbO₂ + SO₄²⁻ + 4H⁺ + 2e⁻ → PbSO₄ + 2H₂O

Equations show that lead is oxidized and lead dioxide is reduced during discharging phase. Electrical energy is produced during this process. This reaction is enabled due to presence of sulfuric acid which provided sulfate ions to react at both electrodes.

Charge Reactions:

• At the negative plate: PbSO₄ + 2e⁻ → Pb + SO₄²⁻
• At the positive plate: PbSO₄ + 2H₂O → PbO₂ + SO₄²⁻ + 4H⁺ + 2e⁻

If you compare charging and discharging equations side by side, it becomes evident that during charging phase, discharging reactions are reversed and electrical energy is absorbed. Lead and lead dioxide is formed again at respective electrodes. Sulfate ions are also restored which will form sulfuric acid.

Both charging and discharging reactions are enabled by acid. Negative and positive electrodes are immersed in diluted sulfuric acid, though separated by a porous synthetic material.

Battery Acid in Automobiles:

With technological advancements in automotive sector, demand and requirements for vehicle batteries also changed drastically. Electrical loads of vehicles kept increasing and battery manufacturers responded accordingly and improved battery material, design, and quality of electrolyte. Lead acid batteries are used in automobiles mostly (alternatives are there but lead-acid batteries are preferred over other options) and so electrolyte is always sulfuric acid.

For automotive batteries, 37% concentration of sulfuric acid has emerged as a standard. This concentration is vital for ensuring good performance and prolonged life of battery and battery cells. There are some ways, 37% concentrated sulfuric acid helps gain key advantages.

• Density is an important parameter for electrolyte and it affects battery’s capability to generate and store charge. At 37% concentration of sulfuric acid, electrolyte’s specific gravity helps maintain safety as well as performance.
• At 37% concentration, sulfuric acid ensures good ion mobility and effective electrochemical reactions.
• Diluted sulfuric acid decreases the risk of undesirable side reactions which might degrade internal components of a battery.

Is Battery Acid Harmful and How to Handle it?

Though, battery acid is diluted; nonetheless, it could be very harmful for skin and other body parts. It is corrosive in nature so it can cause itching, redness, burning, or pain on your skin. In case of exposure with battery acid, you must wash the affected skin patch with running and cool water for few minutes. If acid splashes into your eyes, somehow, it can affect vision and even lead to permanent blindness. Swallowing of acid can damage internal organs severely and cause death (in some cases). Acids emit harmful vapors causing respiratory problems which might also cause medical emergency for you.

Here are some tips, you should follow, while storing, replacing, or handling acid or acid bases batteries:

• Keep them away from the reach of children
• You must wear PPE (Personal Protective Equipment) which includes acid-resistant gloves, clothing, and safety goggles.
• Battery must be kept in properly ventilated area so excessive gases don’t accumulate posing risk of inhalation, explosion, and ignition.
• Sparks and flames must be kept away from acid batteries as emission of hydrogen gas from these batteries might catch fire.
• If acid spills, somehow, don’t wipe or clean it directly. Instead, neutralize it with some basic substance first. Baking soda is a common product which can be found easily and has basic effect (pH above 7).

Why Use High Quality Acid for Your Battery?

As demand for sustainable energy resources is increasing, need for quality batteries is also going up. Battery manufacturers and researchers have developed batteries where change in design and material have helped them boost battery performance. Acid, being an important component, does also impact performance of a battery cell heavily. If you choose to use high quality electrolyte in form of acid, you can expect:

• More dependable and consistent performance for wide range of temperature and other conditions.
• High quality acid is less prone to stratification and also helps reduce water losses which can cause irregular performance.
• Using high quality acid will also help your product meet respective industry standards about recyclability and emissions.
• Quality acid also ensures minimal chances of leaks, corrosion, and degradability of casings and seals.
• Efficient electrochemical reactions and utilization of battery’s full capacity without frequent self-discharging.
• Use of poor quality acid might lead to premature failures and battery replacements because impurities (organic compounds and metal ions) will interfere with above mentioned reactions.
• With low quality acid, Capacity will diminish and hinder battery’s capability to perform heavy tasks like engine starting in automotive. This might be because of buildup of deposits like lead sulfate crystals.
• High quality acid ensures that battery would operate safely by preventing production of excessive hydrogen that could lead to explosion and ignition

What is Meant by Testing of Battery Acid?

To monitor and evaluate health of a battery, many tests are there. These tests involve checking capacity, life cycle, voltage etc. for a battery. Here, our focus is just on battery acid. So we will be discussing purpose of testing battery acid, types of tests, and outcomes of tests.

For battery acid or any other electrolyte, specific gravity is monitored which gives an idea about its charging level. As battery discharges, density of acid keeps decreasing. So, by checking specific gravity of sulfuric acid, you get to know about its charging level. A thorough test and evaluation helps determine if battery can be exchanged or maintenance would serve the purpose.

Ways to Measure Specific Gravity of Battery Acid:

To measure specific gravity of battery acid, you can use

1. Hydrometer, also known as aerometer

Or

1. Digital hydrometer, also known as digital density meter

Hydrometer looks like a syringe attached with bulb. Calibrations are made on float residing within bulb. Upon sucking some acid from battery, you can see reading to know specific gravity. Digital density meter can measure density if it could withstand strong acidic effect. It converts the result into the desired temperature and units and displays it.

Hydrometer has lower price compared to that of digital density meter. Anyhow, analog one is not much accurate; due to manual reading, errors are likely. Aerometer is breakable easily and needs large amount of acid from battery as sample.

On the other hand, digital hydrometer has high price but it comes with several advantages. It has built-in manual pump which can be filled easily and is safe to use. This density meter needs very little amount of electrolyte as sample. It is highly accurate as it comes with integrated conversion table which can measure density and calculate specific gravity automatically.

Checking Acid Level:

Acid or electrolyte level is another important factor which affects battery performance largely. Ideally, all battery cells shall be submerged in diluted battery acid. To check acid level, plastic covers shall be removed. Area around the ports or openings shall be cleaned. Underneath dirt shall also be cleaned. Now, shed the light so electrolyte level and cells become visible. If acid level is low and cells are uncovered, pour distilled water to raise electrolyte level until cells get covered.

Safety Precautions While Checking Battery Acid:

Safety measures are very important while working with any kind of battery. If battery is acid based, then precautionary measures become more essential. All safety measures are mentioned above; anyhow, a recap is given here with respect to acid testing.

While dealing with acid, gloves, protective clothing, and goggles must be worn so acid splashes, won’t harm your skin, and eyes. Battery must be kept in ventilated area and maximum possible distance shall be maintained so acid fumes don’t enter respiratory system. While cleaning battery or acid spilled out of battery, don’t use any cloth. Instead, use a wired or handled brush.

Conclusion:

Battery acid is an important component in the battery that takes part in electrochemical reactions actively. It also facilitates effective working of battery. Diluted acid is used in lead acid batteries. Handling batteries and, specifically, acid based batteries needs special attention and safety measures which are discussed in detail. Use of diluted sulfuric acid in automotive sector has gained much attention because of reliability and safety provided by lead acid batteries. Use of analog hydrometer and digital density meter is also discussed to help understand testing procedure and requirements. Both tools have their own pros and cons. Importance of monitoring electrolyte level in acid batteries can’t be ignored. Refilling electrolyte level to desired level with appropriate care and safety measures is also important for users and technicians.