Lead-Acid Batteries

History of the Lead-Acid Battery

Invented in 1859 by French physicist Gaston Planté, lead-acid batteries are the oldest type of rechargeable battery.

Planté began experiments that resulted in the construction of a battery for the storage of electrical energy. His first model contained two sheets of lead, separated by rubber strips, rolled into a spiral, and immersed in a solution containing about 10 percent sulfuric acid. A year later he presented a battery to the Academy of Sciences consisting of nine elements, housed in a protective box with the terminals connected in parallel. Remarkably, his battery delivered large currents.

How Lead-Acid Batteries Work

All lead-acid batteries consist of two flat plates—a positive plate covered with lead dioxide and a negative made of sponge lead—that are immersed in a pool of electrolyte (a combination of sulfuric acid (35%) and water solution (65%). Electrons are produced from the chemical reaction producing voltage. When there is a circuit between the positive and negative terminals, electricity begins to flow, providing connecting sources with power.

A lead-acid cell produces voltage by receiving a (forming) charge of at least 2.1 volts/cell from a charger. Known as Storage Batteries, lead-acid batteries do not generate voltage on their own/ they only store a charge from another source. The size of the battery plates and amount of electrolyte determines the amount of charge lead-acid batteries can store.

Storage capacity is described as the amp hour (AH) rating of a battery. In a typical lead-acid battery, the voltage is approximately 2 volts per cell, for a total of 12 volts or a rating of 125 AH, which equates to the battery's ability to supply 10 amps of current for 12.5 hours or 20 amps of current for a period of 6.25 hours.

Batteries are in a constant process of charge and discharge, discharging when connected to a load needing electricity such as a car starting and/or an accessory pulling a charge. A battery becomes charged when current flows back into it, restoring the chemical difference between the plates.

The lead plates become more chemically alike when a battery discharges, causing the acid to weaken and the voltage to drop. The battery will eventually become so discharged that it loses its ability to deliver useful voltage.

A battery, however, can be recharged by feeding it electrical current—restoring the chemical difference between the plates and returning the battery to full operational power.

Operational problems and failure have plagued lead-acid batteries since their invention more than 100 years ago. Through the years, science has improved materials, manufacturing methods and overall performance, however, the demand on lead-acid batteries continues to grow with a plethora of onboard gadgets drawing down on the power source, literally sapping batteries like a parasitic vampire. The lifespan of today's lead-acid battery typically ranges from as little a 6 months to 48 months—though only 30% survive the entire four years.


Lead-acid batteries are in a constant process of charge or discharge. If the battery is not being charged or maintained then it is discharging. In order to store energy within the battery, there are continuous chemical reactions occurring. This means that unused batteries also exhibit a slow discharge – even newly manufactured ones.

In theory, lead-acid batteries should last many years, but they usually don't because of a series of detrimental problems caused by excessive sulfation buildup related to the natural and necessary formation of sulfate crystals on the surface of lead battery plates. Over time as the battery is discharged, the electrolyte turns to water and the lead plates become covered with lead sulfate. This reaction is known as sulfation. If the battery is not being charged or maintained then it is discharging.

A lead sulfate is a crystalline material that starts as a small nucleus and enlarges over time into larger and larger crystal formations. These larger crystals have stronger bonds that require more energy to break. They form over longer periods of time. The longer the battery discharges, the stronger the bonds are that form and at some point it becomes impossible to remove the lead sulfate. At this point the battery is dead with no possibility of being recovered. In fact, 80% of the batteries in use worldwide 'die' prematurely due to this excessive sulfation buildup.

PulseTech's patented Pulse Technology has been scientifically proven to remove naturally occurring lead sulfates from the battery plates and return them to electrolyte solution. Used consistently, Pulse Technology will prevent the larger crystals from forming allowing more room in the battery to store energy which in turn allows the battery to accept, store and release maximum energy.

Lead-acid Battery Types

There are two basic types:

These batteries start engines on cars, boats and other vehicles. They provide a short burst of strong power to get the engine started.

Deep Cycle
These batteries, used for industrial purposes, provide low, steady power over a period of time opposed to the instant burst of energy providing by starting battery types. The plates are much thicker and there is usually much more total energy available for a longer period of time.

Battery Construction Types

VRLA (Value Regulated Lead-Acid)
This type of battery is sealed and Maintenance Free. It uses special pressure valves and should never be opened. The valve(s) open when a preset pressure is realized inside the battery and lets the excess gas pressure out; the valve then resets itself. They are commonly composed of two types:

  1. AGM (Absorbed Glass Mat)
    AGM sealed battery technology was originally developed in 1985 or military aircraft. AGM technology has continued to develop and offer improvements over other sealed battery technologies. AGM is considered the next step in the evolution of both starting and deep cycle sealed batteries for marine, RV and aviation applications, delivering increased safety, performance, and service life over all other existing sealed battery types, including gel technology. In AGM sealed batteries, the acid is absorbed between the plates and immobilized by a very fine fiberglass mat. No silica gel is necessary. This glass mat absorbs and immobilizes the acid while still keeping the acid available to the plates. This allows a fast reaction between acid and plate material.

    The AGM battery has an extremely low internal electrical resistance. This, combined with faster acid migration, allows the AGM batteries to deliver and absorb higher rates of amperage than other sealed batteries during discharging and charging. In addition, AGM technology batteries can be charged at normal lead-acid regulated charging voltages, therefore, it is not necessary to recalibrate charging systems or purchase special chargers.
  2. Gel Cell
    Gelled batteries or "Gel Cells" contain acid that has been "gelled" by the addition of Silica Gel, turning the acid into a solid mass thus making it impossible to spill acid even if they are broken. The recharge voltages on this type of cell are lower than the other styles of lead-acid battery to prevent excess gas from damaging the cells. This is not usually a problem with solar electric systems, but if an auxiliary generator or inverter bulk charger is used, current must be limited to the manufacturer's specifications. Gel batteries are best used in very deep cycle application and may last a bit longer in hot weather.

Wet Cell (flooded)
Most automotive batteries are wet cell, which operate by means of a liquid electrolyte solution. They come in two basic types—serviceable and maintenance free. The flooded battery typically delivers a peak current of 450 amps. An improved type of wet cell is the sealed valve regulated lead-acid (BRLA), which is popular in the automotive industry as a replacement for the lead-acid wet cell. The Valve Regulated Lead-acid (VRLA) battery uses an immobilized sulfuric acid electrolyte, reducing the chance of leakage and extending shelf life.

Care and Routine Maintenance

There are eight major reasons for pre-mature battery failure:

  1. Battery self-discharge
  2. Key off parasitic drain
  3. Insufficient run time
  4. Corroded battery terminals and cables
  5. Intermixing of un-matched batteries
  6. Operator error
  7. Faulty electrical systems
  8. Physical damage

A battery that's at the end of its service life can't be recharged enough to restore it to a useful power level and must be replaced.

However, a battery that has been attacked by microscopic sulfate crystals inhibiting the battery's ability to create, store and release energy, is a battery typically worth saving. It's common for people to assume a sulfated battery is 'dead' when it can't be recharged with a regular charger. However, battery recovery chargers using Pulse Technology have a 70%+ success rate of reviving these types of batteries.


State of Health
It means how much battery capacity is left (%) comparing with the marked original battery capacity

State of Charge
Is a measurement of voltage currently in the battery. It's usually stated as a percent of full charge.

CCA (Cold Cranking Amps)
This is the SAE (Society of Automotive Engineers) measurement that should be entered into the battery tester for test purposes. It is defined as the current in amperes which a new fully charged battery can deliver for 30 seconds continuously without the terminal voltage falling below 1.2 volts per cell, after it has been cooled to 0°F and held at that temperature. This rating reflects the ability of the battery to deliver engine-starting currents under winter conditions.

The unit of measurement of electrical capacity. A current of one ampere for one hour implies the delivery or receipt of one ampere-hour of electricity. Current multiplied by time in hours equals ampere-hours.


Nationally, 2,300 people are injured each year using lead-acid batteries. Acid burns to the face and eyes comprise about 50% of these injuries as these batteries can explode. The remaining injuries were mostly due to lifting or dropping batteries.

Safety Basics

  • The electrolyte is a solution of sulfuric acid and water. This solution can cause chemical burns to the skin and especially the eyes.
  • During normal operation, water is lost from a non-sealed (or flooded) battery due to evaporation.
  • During charging, lead-acid batteries produce hydrogen and oxygen gases (highly flammable/explosive) as electrolysis occurs.
  • Many lead-acid explosions are believed to occur when electrolytes are below the plates in the battery and thus, allowing space for hydrogen/oxygen to accumulate. When the battery is engaged, it may create a spark the accumulated gases and causes the battery to explode.

Standard Precautions

  • Always store or recharge batteries in a well ventilated area away from sparks or open flames
  • Damaged lead-acid batteries should be kept in properly labeled acid-resistant secondary containment structures
  • Use only chargers that are designed for the battery being charged
  • Always keep lead-acid battery vent caps securely in place
  • Do not store acid in hot locations or in direct sunlight
  • Pour concentrated acid SLOWLY into water, do not add water into acid
  • Use non-metallic containers and funnels
  • If acid get into your eyes, flush immediately with water for 15 minutes, and then promptly seek medical attention
  • If acid gets on your skin, rinse the affected area immediately with large amounts of water. Seek medical attention if the chemical burns appear to be second degree or greater
  • Never overcharge a lead-acid battery and only replenish fluid with distilled water
  • Emergency was stations should be located near lead-acid battery storage and charging areas
  • Prevent open flames, sparks or electric arcs in charging areas
  • Lead-acid storage and charging areas should be posted with "Flammable- No Smoking" signs
  • Neutralize spilled or splashed sulfuric acid solution with a baking soda solution, and rinse the spill area with clean water

Servicing Recommendations

  • Keep metal tools and jewelry away from the battery
  • Inspect for defective cables, loose connections, corroded cable connectors or battery terminals, cracked cases or covers, loose hold-down clamps and deformed or loose terminal posts
  • Replace worn or unserviceable parts
  • Check the state of charge of non-sealed and sealed batteries with an accurate digital voltmeter when the engine is not running, and lights and other electrically powered equipment are turned off. Also check the electrolyte levels and specific gravity in each cell of non-sealed batteries
  • When checking the electrolyte liquid levels of the batteries use a rated flashlight that is intrinsically safe. In the event one is not available, use a plastic/non-metallic flashlight. Turn on the flashlight prior to getting near the battery when checking cell levels and turn off the flashlight when you are away from the batteries
  • Follow the battery manufacturer's recommendations about when to recharge or replace batteries
  • Tighten cable clamp nuts with proper size wrench. Avoid subjecting battery terminals to excessive twisting forces
  • Use a cable puller to remove a cable clamp from the battery terminal
  • Remove corrosion on the terminal posts, hold down tray and hold down parts
  • Use a tapered brush to clean battery terminals and the cable clamps
  • Wash and clean the battery, battery terminals, and case or tray with water. The corrosive acid can be neutralized by brushing on some baking soda (sodium bicarbonate) solution. If the solution does not bubble, the acid is probably neutralized
  • To prevent shocks, never touch or come in contact with both terminals at the same time. If baking soda solution is applied with a cloth, remember that these solution can conduct electricity
  • When battery cables are removed, ensure that they are clearly marked "positive" and "negative" so that they are reconnected with the correct polarity
  • Use a battery carrier to lift a battery, or place hands at opposite corners. Remember, batteries can weigh 30 to 60 pounds, so practice safe lifting and carrying procedures to prevent back injuries
  • Never fill battery cells about the level indicator
  • Do not squeeze the syringe so hard that the water splashes acid from the cell opening

Frequently Asked Questions

Do lead-acid batteries discharge when not in use?

All batteries, regardless of their chemistry, will self-discharge. The rate of self-discharge for lead-acid batteries depends on the storage or operating temperature. At a temperature of 80 degrees Fahrenheit a lead-acid battery will self-discharge at a rate of approximately 4% a week. A battery with a 125-amp hour rating would self-discharge at a rate of approximately five amps per week. Keeping this in mind, if a 125 AH battery is stored for four months (16 weeks) winter without being charged, it will lose 80 amps of its 125-amp capacity. It will also suffer from severe sulfation, inhibiting the plates from accepting and distributing a charge. Keep batteries maintained.

Do lead-acid batteries develop a memory?


Do I need to completely discharge my lead-acid battery before recharging it?

No. You should never discharge your lead-acid battery below 80% of its rated capacity. Discharging below this point or 10.5 volts can damage it.

Will routine pulse maintenance benefit other electrical components on my boat or vehicle?

Yes. By maintaining your batteries in peak conditions, your alternator does not have to work as hard at recharging your vehicle's battery once it has started. The battery will accept a charge more eagerly and more quickly so alternator life should be extended. Plus, by maintaining available cranking amps in your battery, there will be more available energy going to your starter. The engine will turn over faster, so your starter should last longer as well.

Will weather affect my battery?

Yes. What many people don't realize is that extreme cases of heat and cold will increase the speed of sulfation buildup and the rate of discharge within a battery. For example, when the weather starts to get hotter, the rate of sulfation buildup will actually double for every 10-degree increase in temperature. That means that if the temperature goes from 75° to 95°, sulfation buildup on battery plates will occur 400% faster than normal. So... batteries stored or in vehicles in warm weather have the potential to fail due to the build up of sulfation, much sooner than batteries stored or in vehicles in cooler weather.

Cold weather, this is a real "Domino Effect"...When it's cold outside, sulfation buildup in combination with the slow down of the chemical reaction within the battery will rob the batteries ability to provide operational power and is only exaggerated as vehicle fluids thicken due to the cold. This cold condition causes even more available power and capability to be taken from the battery to start the vehicle, so the battery has to work harder than normal to provide additional power demanded by the vehicle and as a result realizes a further reduction in voltage causing faster buildup of sulfates on the lead plates. Also, keep in mind that the battery's electrolyte can actually freeze if the battery is in an advanced state of discharge, and this could physically damage the lead plates. At 1.270 specific gravity (100% charged) battery acid will freeze at -83°F, at 1.200 it will freeze at -17°F and at 1.140 (completely discharged) it will freeze at only 8°F.

Is it possible to recover a discharged battery that will no longer accept a charge?

Yes. Use a Battery Analyzer to determine if the battery is a good candidate for recovery (Note: Even though the analyzer may read "REPLACE BATTERY," it could still be recoverable.) We have smart charges that will analyze, charge and recover all types of lead-acid batteries. Keep in mind that some very badly sulfated battery plates could take several days to clean. Also, not all batteries can be totally recovered. If a battery has a short circuit or physical damage, it is impossible to bring back.

By helping keep plates clean, the battery works harder than ever thought possible. It maintains a greater reserve capacity, will recharge faster and release more of its stored energy. With more available energy, battery output is maximized between charges, and electronic accessories work better.