Can the Lead-acid Battery Compete in Modern Times?

The answer is yes. Lead-acid is the oldest rechargeable battery in existence. Lead acid was invented in 1859 by the French doctor Gaston Planté, and it was the first rechargeable battery for commercial use. 150 years later, we still do not have cost-effective alternatives for cars, wheelchairs, scooters, golf carts and UPS systems. Lead-acid batteries still maintain market share in applications where newer battery chemistries are too expensive.

Lead acid cannot make it charge quickly. The typical charging time is 8 to 16 hours. Regular full saturation of charge is essential to prevent sulfates, so the battery must always be stored in a charged state. Leaving the battery in a discharged state will cause sulfation and may not be able to charge.

The competitiveness of lead-acid batteries

Finding the ideal charging voltage limit is crucial. High voltage (higher than 2.40V/battery) can produce good battery performance, but the service life is shortened due to the corrosion of the grid on the positive plate. The low pressure limit will cause sulfation on the negative plate. Leaving the battery in a floating state for a long time will not cause damage.

Depending on the depth of discharge and operating temperature, sealed lead acid can provide 200 to 300 discharge/charge cycles. The main reason for its relatively short cycle life is the corrosion of the positive electrode grid, the exhaustion of the active material and the expansion of the positive plate. These changes are most common at higher operating temperatures. Cycles will not prevent or reverse trends.

Plate thickness

The service life of lead-acid batteries can be measured in part by the thickness of the positive plate. The thicker the plates, the longer the service life will be. During the charging and discharging process, the lead on the board is gradually eaten, and the deposit falls to the bottom. The weight of the battery is a good indicator of the lead content and life expectancy.

The thickness of the electrode plate of a car starter battery is about 0.040 inches (1 mm), while the thickness of a typical golf cart battery is between 0.07-0.11 inches (1.8-2.8 mm). The forklift battery plate may exceed 0.250 inches (6 mm). Most industrial deep-cycle batteries use lead antimony plates. This can extend the life of the plate, but it will increase out gassing and water loss.

Sealed Lead-acid

In the mid-1970s, researchers developed maintenance-free lead-acid batteries that could be operated in any location. The liquid electrolyte gels into a wet diaphragm and seals the casing. The safety valve allows exhaust when inflation, exhaust and atmospheric pressure change.

Driven by different market demands, two types of lead acid systems have emerged: small sealed lead acid (SLA) and the larger Valve regulated lead acid (VRLA). Both batteries are similar. Engineers may argue that the term “sealed lead acid” is improperly used because the rechargeable battery cannot be completely sealed.

Unlike flooded lead-acid batteries, both SLA and VRLA are designed with a low overvoltage potential to prevent the battery from reaching the gas-generating potential during the charging process, because overcharging will cause out gassing and water consumption. Therefore, these batteries can never be fully charged. To reduce drying out, sealed lead-acid batteries use lead calcium instead of lead antimony.

The best working temperature for lead-acid batteries is 25°C (77°F). High temperature will reduce service life. In principle, every 8°C (15°F) increase in temperature will reduce battery life by half. VRLA can last for 10 years at 25°C (77°F). If it is operated at 33°C (92°F), it can only be used for 5 years. If a constant desert temperature of 41°C (106°F) is maintained, the same battery will fail after 2.5 years.

The rated discharge time of sealed lead-acid batteries is 5 hours (0.2) and 20 hours (0.05C). Longer discharge times produce higher capacity readings because of lower losses. Lead acid performs well under high load currents.

Absorbed glass mat battery (AGM)

AGM is a new type of sealed lead acid that uses absorbent glass pads between the plates. It is sealed, maintenance-free, and the board is firmly installed to withstand a wide range of shocks and vibrations. Almost all AGM batteries are recombinant, which means they can recombine 99% of oxygen and hydrogen. There is almost no water loss.

The charging voltage is the same as other lead-acid batteries. Even under severe overcharge conditions, hydrogen emissions are lower than 4% of the aircraft and enclosed space regulations. Low self-discharge of 1-3% per month can be stored for a long time before charging. The price of AGM is twice that of the flooded version of the same capacity. Due to durability, German high-performance cars use AGM batteries instead of flooded type batteries.

Advantages and limitations of lead-acid batteries

Advantages

• Cheap and easy to manufacture.

• Mature, reliable and easy-to-understand technology-the correct use of lead acid can be durable and provide reliable services.

• Self-discharge is the lowest among rechargeable battery systems.

• Able to achieve high discharge rate.

Limitations

• Low energy density-poor weight/energy ratio limits fixed and wheeled applications.

• Do not store in a discharged state-the battery voltage must never drop below 2.10V.

• Allows only a limited number of full discharge cycles-ideal for standby applications that require only occasional deep discharge.

• Transport restrictions for lead-acid flooding-Leakage involves environmental issues.

• Improper charging may cause thermal runaway.

In summary, although lead-acid batteries have many limitations, they still have many advantages. As lead-acid batteries continue to make progress to adapt to the entire market, they occupy a large share of the market they and have a certain degree of competitiveness in modern time.