Master Electrician

Lead-acid batteries remain the most common battery type in electrical installations, particularly for backup power, emergency lighting, and uninterruptible power supplies. The chemistry involves lead dioxide (PbO₂) as the positive plate, sponge lead (Pb) as the negative plate, and dilute sulfuric acid (H₂SO₄) as the electrolyte.

During discharge, both plates convert to lead sulfate (PbSO₄), and the electrolyte becomes more dilute. During charge, the process reverses. The specific gravity of the electrolyte indicates state of charge: fully charged cells typically measure 1.265 to 1.280; fully discharged cells measure approximately 1.120.

Valve-regulated lead-acid (VRLA) batteries are sealed designs that recombine gases internally under normal operation. Two types exist: absorbed glass mat (AGM) batteries use fiberglass separators to immobilize the electrolyte; gel batteries use silica to convert electrolyte into a gel. VRLA batteries are maintenance-free and can be installed in any orientation except inverted.

Lead-acid battery failure modes include sulfation (formation of large lead sulfate crystals that resist reconversion), stratification (electrolyte density differences between top and bottom), grid corrosion, and active material shedding. Proper charging practices minimize these degradation mechanisms.

Nickel-cadmium (NiCd) batteries use nickel hydroxide as the positive electrode and cadmium as the negative electrode, with potassium hydroxide electrolyte. NiCd cells produce 1.2V nominal and offer excellent cycle life, wide temperature tolerance, and high discharge rates. The primary disadvantage is the memory effect: repeated partial discharges can reduce effective capacity. Cadmium toxicity requires proper disposal procedures.

Nickel-metal hydride (NiMH) batteries replace cadmium with a hydrogen-absorbing alloy. NiMH batteries offer higher energy density than NiCd and reduced memory effect. However, they have higher self-discharge rates and less tolerance for overcharge. NiMH batteries are common in cordless tools and hybrid vehicles.

Both nickel-based chemistries tolerate overcharge better than lithium-ion but have lower energy density. They can be fast-charged and perform well at low temperatures.

Lithium-ion batteries have become dominant in portable electronics and electric vehicles due to high energy density, no memory effect, and low self-discharge. The positive electrode typically consists of lithium cobalt oxide, lithium iron phosphate, or lithium manganese oxide. The negative electrode is typically graphite. The electrolyte is a lithium salt in an organic solvent.

During charge, lithium ions migrate from the positive electrode to the negative electrode and intercalate into the graphite structure. During discharge, the process reverses. This intercalation mechanism gives lithium-ion batteries their name.

Lithium-ion batteries require sophisticated battery management systems (BMS) to prevent overcharge, over-discharge, overcurrent, and thermal runaway. Overcharge can cause thermal runaway and fire. Over-discharge can cause copper dissolution and internal shorts on subsequent charge. Operating temperature must be controlled to optimize performance and safety.

Lithium iron phosphate (LiFePO₄) batteries offer improved safety and longer cycle life compared to lithium cobalt oxide but have lower energy density. They are increasingly common in stationary energy storage applications.