The lead-acid Battery Systems is the oldest rechargeable battery that exists today. Invented by the French physicist Gaston Planté in 1859, it was the first rechargeable lead-acid battery for commercial use. 150 years later, we still don't have profitable alternatives to cars, wheelchairs, scooters, golf carts, and UPS systems. The lead-acid battery has held a large market share in certain applications, if the battery chemistry were more recent it would be too expensive. The Lead-acid battery does not lend itself to fast charging.
Finding the ideal load voltage limit is critical. A high voltage (above 2.40V / cell) produces good battery performance, but shortens the life due to corrosion of the grid on the positive plate. A low voltage limit is subject to sulphation on the negative plate. Leaving the battery on float charge for a long time will not cause damage.
The lead-acid battery does not like deep discharge cycles. A complete discharge causes additional stress and each cycle robs the Battery Systems of life in some services. This wear-down characteristic also applies to other chemical batteries to varying degrees. To avoid battery stress through repetitive deep discharge, a larger battery is recommended. Lead-acid battery is cheap, but running costs can be higher than a nickel-cadmium-based system if repetitive full cycles are required.
Depending on the depth of discharge and operating temperature, sealed lead-acid batteries provide 200 to 300 discharge / charge cycles. The main reason for its relatively short life cycle is the corrosion of the positive electrode grid, the depletion of the active matter and the expansion of the positive plates. These changes are more frequent at higher operating temperatures. Cyclical reloading does not prevent or reverse the trend.
The life of a lead-acid battery can, in part, be measured by the thickness of the positive plates. The thickness of the plates provides a longer life. During loading and unloading, the lead on the plates is slowly eaten away and the sediment falls to the bottom. The weight of a battery is a good indication of lead content and life expectancy.
Automobile starter battery plates are about 0.040 "(1mm) thick, while typical golf cart batteries have plates that are between 0.07-0.11" (1.8-2.8mm) thick. Forklift batteries can have plates that exceed 0.250 "(6mm). Most deep-cycle flooded industrial batteries use lead-antimony plates. This improves the life of the plate, but increases the loss of water and gases.
During the 1970s, researchers developed a maintenance-free lead-acid Battery Systems that can operate in any position. The liquid electrolyte is gelled in separators, moistened and sealed. Safety valves allow ventilation during loading, unloading and changes in atmospheric pressure.
Driven by different market needs, they suggested two lead-acid systems: the small sealed lead-acid battery (SLA), also known as Gelcell, and the larger valve-regulated lead-acid battery (VRLA). Both batteries are similar. Engineers can argue that the word "acid" is a misnomer in sealed lead batteries because no rechargeable battery can be fully sealed.
Unlike flooded lead-acid batteries, SLAs and VRLAs are designed with low potential excess voltage to prevent the battery from reaching its gas-generating potential during charging because over-charging could cause gassing and the depletion of water. Consequently, these batteries cannot be charged to their full potential. To reduce dryness, sealed lead-acid calcium batteries use lead instead of lead-antimony.
The optimum operating temperature for the lead-acid battery is 25 ° C (77 F *). At elevated temperature it reduces longevity. As a guideline, every 8º C (15 F *) increase in temperature will reduce the battery life by half. A VRLA, which would last 10 years at 25 ° C (77 F *), will only be good for 5 years if operated at 33 * C (95 F *). In theory, the same battery would last a little over a year at a desert temperature of 42 ° C (107 * F).
Sealed lead-acid batteries are rated at about 5 hours (0.2) and 20 hours (0.05C) discharge. Longer discharge times make higher capacity readings due to lower losses. The lead-acid battery works well with high charge currents.
Batteries with absorbent glass separator (AGM)
AGM is a new type of sealed lead-acid Battery Systems that uses absorption glass mats between plates. It is sealed, maintenance-free and the plates are rigidly mounted to withstand heavy shocks and vibrations. Almost all AGM batteries are recombinant, which means that they can recombine with 99% of oxygen and hydrogen. There is almost no water loss. The charging voltages are the same as for other lead acid batteries.
Even under severe overload conditions, it emits hydrogen below the 4% set for airplanes and enclosed spaces. The low self-discharge of 1.3% per month allows for long-term storage before recharging. AGM costs are double that of the flooded version of the same capacity. Due to durability, high-performance German cars use AGM batteries in favor of the flood type.