How Does the Lead Acid Battery Work?

The first commercially available rechargeable battery was invented in 1859 by a French doctor named Gaston Plante. Although the lead-chemical battery is ancient and outdated, it is still widely used today. The lead-chemical battery is popular because of its cost-per-watt basis and the reliability and cheapness of lead acid. And few other batteries can provide large volumes of power as cheaply as lead-acid batteries, making them cost-effective for golf carts, ships, cars, forklifts, and uninterrupted power.

The grid structure in the lead-acid battery is made of lead alloy. Because pure lead is too soft to support itself, small amounts of other metals are added to the mix for higher mechanical strength and improved electrical performance. In addition, the most common additives are antimony, tin, calcium, and selenium. These batteries are often called “lead-antimony batteries” or “lead-calcium batteries.”

Antimony and tin were added to improve the deep circulation but at the same time increased consumption and increased the need for balance. The role of calcium is to reduce self-discharge, but lead-calcium plates also have specific side effects, such as overcharging, due to the growth of mesh oxidation. Modern lead-acid batteries also use selenium, arsenic, tin, and cadmium as dopants to degrade antimony and calcium.

Because of its heavy weight, lead acid is slightly less durable than nickel and lithium-based systems during deep cycles. The strain occurs during full discharge and permanently strips the battery of a small capacity with each release or charge cycle. But this loss is slight when the battery is in good working condition but increases once the performance drops to standard nominal capacity. This kind of wear applies to all batteries to varying degrees.

According to the discharge depth, the deep cycle application of lead acid can provide 200 to 300 discharge or charging cycles because of the positive grid corrosion, active material exhaustion, positive plate expansion, and other reasons, so its cycle life is short. This aging phenomenon is accelerated at a high discharge current and high operating temperature. (See also: How to extend lead-acid battery life.)

With the proper voltage limits, charging a lead-acid battery is simple. If cold produces poor performance and causes sulfate to build upon the negative plate, the lead-acid battery chooses a low voltage limit to shield the cell. Corrosion on positive plates is improved performance due to high voltage limits. But acidification can be reversed if repaired promptly, but the breakdown is permanent (see charge lead acid).

The fast charging method is not suitable for lead-acid batteries, and most lead-acid batteries need 14-16 to be fully charged at a time. Battery storage can only be done when fully charged. Acidification is caused by low charge, which can also damage battery performance. Still, a lead-acid battery can solve this problem by adding carbon to the negative electrode to reduce this problem and reduce the specific energy. (See new lead-acid system.)

Lead-acid batteries also have an average life span, are not as affected by memory as Negi batteries, and remain the most lit of the rechargeable battery types. NiCd loses about 40% of its stored energy in three months, but lead acid produces the same power in a year. Lead-acid batteries work well at low temperatures and perform well at sub-zero temperatures. According to data from a 2018 study by RWTH Aachen University in Germany, water-flooded lead-acid batteries are about $150 per kWh, one of the lowest battery costs.

Sealed Lead Acid

In the mid-1970s, the first sealed and maintenance-free lead-acid batteries appeared. Engineers think it’s a misnomer to call it “sealed lead acid” because no lead-acid battery can be completely sealed. Valves are added to control venting during pressure charging and rapid discharge, and gas release can occur when pressure increases. The electrolyte is impregnated in a wet separator rather than in liquid. The design is similar to nickel and lithium-based systems, making it impossible for the 2-operated battery to leak in any physical direction.

Sealed cells have fewer electrolytes than submerged ones, known as “acid-deficient” cells. Combining oxygen and hydrogen to form water and preventing drying during circulation are the most significant advantages of sealed lead acid. Recombination occurs at a moderate pressure of 0.14 bar (2psi). The valve is used as a safe outlet when gas accumulates and rises. To avoid eventual drying, avoid repeated venting. According to data from RWTH Aachen University in Germany in 2018, VRLA costs about $260 per kWh.

Several sealed lead-acid batteries have emerged, the most common of which are gel cells, also known as valve-controlled lead acid (VRLA) or absorbent glass pad (AGM). The gel cell contains a silica-type gel that suspends the electrolyte in a paste. SLA(sealed lead acid) is a small package with a capacity of up to 30Ah. The batteries, packaged in a plastic container, can be used in small UPS, wheelchairs, and emergency lighting. Sales remain the preferred choice for healthcare in hospitals and nursing homes because of their reliable service and low cost of ordering and maintenance. The type of power backup used for cellular relay towers, hospitals, Internet centers, banks, airports, etc., is the larger VRLA.

The AGM’s suspension of the electrolyte in a specially designed glass pad offers some advantages to the lead-acid system and instantaneous high load current and faster-charging speed. AGM is a mid-range battery with a capacity of 30 to 100Ah, so it is most suitable for unstable and large systems such as UPS. Typical examples are start-stop functions for micro-hybrid cars, start batteries for motorcycles, and ships and RVs that require some bicycles.

AGM capabilities decline with cycle and age. Gel-type batteries have a dome-shaped performance curve, so they stay in the high-performance range for longer but then drop abruptly to the end of their lives. AGM is cheaper than gel but more expensive than oil. (Gel is too costly to start and stop a car.)

Sealed lead-acid batteries have a low overvoltage potential, different from flooding, to prevent the battery from reaching gas production potential during charging. Gas, exhaust, and subsequent moisture are depleted and dried by excessive charging. Therefore, for some AGMs, the limit of the gel charging voltage must be set to a state below flooding and cannot be charged to its full potential. The same applies to floating charging when fully charged. Gels and AGM are not a direct substitute for water flooding types in terms of setting. After 24 hours of charging, if no dedicated charger is provided for AGM with low voltage Settings, the lead-acid battery must disconnect from the charger. This prevents emissions due to high floating voltage Settings. (Charge lead acid)

25°C(77°F) is the optimal operating temperature for valve-controlled batteries, and battery life decreases by half for every eight °C(15°F) increase. (See how battery life is affected by heat and load). 5 h (0.2c) and 20 h (0.05c) are rated discharge rates for lead-acid batteries. The best discharge performance is when the battery discharges slowly, and the capacitance reading is significantly higher than the 1c rate when the battery is discharging slowly. However, lead acid can deliver several C’s of high-pulse current in just a few seconds. As a result, lead acid is well suited as a starter battery, also known as prime-light ignition (SLI). Lead acid is environmentally unfriendly because of its high lead content and sulphuric acid.

Lead-acid batteries are usually classified as power (traction or deep cycle), stationary (UPS), and automotive (starter or SLI) applications.

Starter Batteries

The starter battery was designed to start the engine under instantaneous high power load and make it last for a second or so. Because of the size, although the battery cannot carry out a deep cycle, it can provide a high current. To indicate the energy storage capacity, the rated capacity of the starter battery is Ah or RS(spare capacity). To display the wind that the battery can provide at a low temperature, CCA(cold start ampere) is expressed. Battery voltage shall not be lower than 7.2 V if at -18°C(0°F) for 30 seconds under SAE J537 rated CCA ampere. The 25 – a minute running time of steady discharge is reflected by RC.

The starter battery with low internal resistance is achieved by adding additional plates for maximum surface area (Figure 1). Lead is applied in a spongy form with thin leaves resembling cellular foam, allowing it to expand its surface area further. Because of the short discharge time, the plate thickness, essential for a deep cycle battery, is not so important to charge the battery while on the road.

Figure 1: Starter battery

There are many thin plates in parallel within the starter cell to achieve low resistance and high surface area, and the starter cell is not allowed to cycle deeply.

Deep-cycle Battery

Wheelchairs, golf carts, and forklifts provide continuous power with deep-cycle batteries. Maximum capacity and reasonably high cycle count are achieved through this cell. The battery is designed for cycles, but stresses still occur when fully discharged. The number of cycles is related to the discharge depth (DoD). Ah, or minute is the running time of the deep cycle battery, typically 5 hours and 20 hours of capacity discharge.

Figure 2: Deep-cycle battery

Deep cycle battery running time, generally 5 hours and 20 hours of capacity discharge. Deep cycle batteries have thick plates to improve cycle capacity, and they typically allow about 300 cycles.

Deep-cycle batteries are not interchangeable with starter batteries, and vice versa. One creative old Ninar installed starter batteries in his wheelchair instead of the more expensive deep-cycle ones to save money. Still, they didn’t last long because the thin spongy plates quickly dissolved during repeated deep cycles.

While these devices are heavy and oversized, military vehicles, trucks, buses, and public safety vehicles can use combined start/deep cycle batteries. In short, lead content is proportional to the quality of the storm, and the battery life is also longer. Table 3 compares the typical life of the starter and deep cycle battery during the deep cycle.

Depth of Discharge Starter Battery Deep-Cycle Battery
100% 12–15 cycles 150–200 cycles
50% 100–120 cycles 400–500 cycles
30% 130–150 cycles 1,000 and more cycles

Table 3: Cycle performance of starter and deep-cycle batteries.

Total discharge is 100%, half discharge is 50%, moderate discharge is 30%, then 70% is surplus.

Lead Acid or Li-ion in your Car?

Lead-acid batteries have been the battery of choice since 1912, when Cadillac introduced the starter motor. Thomas Edison tried to replace lead acid with nickel iron (NiFe). Still, lead acid became popular because of its forgiving, crude properties and low cost, and lithium-ion batteries are currently challenging it as a starting battery for cars.

Figure 4 shows the characteristics of lithium ion and lead acid. At the cold start, the two chemicals act similarly. The W/kg value of lead acid is slightly better than that of lead acid, while the cyclic life of lithium ion is greatly improved, and the Wh/kg value of specific energy is also better. At the same time, the dynamic charge acceptance is also very high. But lithium has some drawbacks because of its complex recycling, inferior safety record to lead acid, and higher cost per kilowatt-hour.

Comparison of lead acid and Li-ion as a starter battery.

The lead acid in the starter battery has a strong lead content, good low temperature performance, low cost, good safety record, recycled, and other advantages.

Because lead is toxic, environmentalists want a chemical to replace lead-acid batteries. In Europe, nickel-chromium has been successfully excluded from consumer products, and similar efforts have been made for starter batteries. Lithium ion and nickel metal hydride are two choices, but the price is too high, and low temperature performance is poor. Lead-acid batteries are likely to continue to be the battery of choice because they have a 99 percent recovery rate and pose little harm to the environment.

Table 5 lists the advantages and limitations of standard lead acid batteries today. The table does not include the new lead acid chemistries. (See also BU-202: New Lead Acid Systems)

Advantages · Low price, simple manufacturing process, low cost per watt-hour

· Low self-discharge, lowest in rechargeable batteries

· High specific power, can withstand high imitation point current

· It has good performance at high and low temperature

Limitations · The specific low energy, the weight-to-energy ratio is poor

· The process is slow, taking 14 to 16 hours to thoroughly saturate and recharge

· To prevent thinning, it must be stored in a charged state

· The life cycle is limited, and repeated deep cycles can shorten battery life

· The flooded battery needs watering

· The transport restriction is of flood type

· Not environmentally friendly

Advantages and limitations of lead acid batteries.

Drying systems, while less robust, have advantages over the flooded system.

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