CourseWiki/Engineering Fundamentals/Electrical Systems

Battery Chemistries

Compare primary alkaline, rechargeable nickel, lead-acid and lithium-ion batteries, and the short history behind them.

Capacity, self-discharge and aging are different

A cell is one electrochemical unit. A battery may contain one cell or several. Its chemistry helps determine voltage, mass, charging needs and how well it holds charge.

Self-discharge is loss of stored charge while no load is connected. Aging is loss of the ability to hold or deliver charge, even after recharging. Both depend on the cell design, temperature and storage conditions, so a chemistry name is not a shelf-life specification.

A capacity rating also depends on discharge current, temperature and the voltage at which the test stops. Use the particular cell's data, not a single capacity assigned to every AA or D cell.

Primary alkaline cells suit replaceable, modest loads

Common primary alkaline cells serve devices such as clocks, remote controls and flashlights. They are widely available and retain charge relatively well in storage. Their useful capacity and terminal voltage fall more under heavy loads and cold conditions.

They are not intended to be recharged. Leakage can damage equipment, especially when cells are exhausted or left in storage. Rechargeable-battery memory effect is not a useful concern for a primary cell.

NiCd and NiMH are rechargeable nickel batteries

Nickel-cadmium (NiCd) and nickel-metal hydride (NiMH) use alkaline electrolytes, but they should not be confused with primary alkaline cells.

Two rechargeable nickel families.
Family	Uses and strengths	Limits
NiCd	Legacy cordless tools and industrial backup equipment; capable of substantial discharge currents in suitable designs.	Cadmium is toxic and requires appropriate battery recycling. Repeated partial cycling can cause memory-related voltage depression. Self-discharge matters during storage.
NiMH	Rechargeable consumer cells and hybrid-vehicle packs; generally more capacity than comparable NiCd cells and no cadmium.	Conventional cells can self-discharge noticeably; low-self-discharge versions improve charge retention. Voltage depression can occur, but memory concerns are generally less pronounced than with NiCd.

Use a charger designed for the chemistry and cell. Fast charging is appropriate only when the cell and charger support it. Do not deliberately drive a pack to zero volts to prevent memory effect: a weaker cell can be forced into reverse polarity by the others.

Why a remote-control recommendation needs more than a chemistry name

A low average load makes charge retention important, but it does not by itself select NiCd over NiMH. Compare the actual cells' self-discharge, usable capacity, voltage and charging requirements. A low-self-discharge NiMH cell behaves differently from an older conventional NiMH cell.

Lead-acid trades low mass efficiency for useful power and cost

Lead-acid batteries appear in engine starting and stationary backup supplies. They can deliver high starting currents and are relatively inexpensive, but they are heavy for the energy stored.

They self-discharge during storage. Prolonged storage while discharged promotes sulfation, which can reduce capacity; this is not the NiCd memory effect. Starting and deep-cycle designs serve different loads. Use the specified charging method: the electrolyte is acidic, lead is toxic, and charging can release gas. Flooded, absorbed-glass-mat and gel designs all exist; modern lead-acid does not always mean gel.

Lithium-ion needs protection; LiPo is not automatically better

Lithium-ion batteries power portable electronics, tools and electric vehicles. Their energy per unit mass is generally considerably higher than NiMH, with relatively slow self-discharge and no routine need for full discharge to prevent memory effect. They still lose capacity through calendar aging and cycling.

Protection and charge control must keep voltage, current and temperature within the cell's limits. A bare cell may not contain its own protection circuit. The pack design must provide the required protection; a protection circuit is not a substitute for a compatible charger.

Lithium-ion polymer, often called LiPo, commonly appears as a light pouch cell in portable devices and model aircraft. The packaging allows thin shapes; some designs support high discharge rates. It does not guarantee higher energy density, lower cost or better resistance to physical damage. Pouches need protection against puncture and crushing. Self-discharge and memory behaviour are broadly those of lithium-ion.

Nominal voltage and charging limits depend on the particular chemistry and cell. Do not use a single voltage for every lithium-ion battery, and do not confuse rechargeable lithium-ion with primary lithium-metal cells.

Battery history moves from a pile to portable rechargeable cells

The important sequence is the change in what batteries made possible.

Volta, around 1800: the voltaic pile made a sustained electrochemical source practical to demonstrate.
Gaston Planté, 1850s: lead-acid introduced a rechargeable battery.
Carl Gassner, 1880s: dry-cell development made the electrolyte easier to contain for portable use. “Dry” means immobilized electrolyte, not absence of moisture.
Waldemar Jungner, 1890s: nickel-cadmium added another rechargeable chemistry.
Lewis Urry, 1950s: work on the modern alkaline cell improved portable primary batteries.
Lithium-ion, 1990s: commercialization enabled rechargeable products with high energy per unit mass, building on earlier work by several researchers.

Scope of this short chronology

This overview uses the historical sequence in the course generation-and-storage notes, with dates rounded to eras. Invention, patent and market introduction are different milestones; the dates are not intended as a priority claim. The development of lithium-ion was a multi-researcher effort, not solely the work of the company that first sold it.

Appears in

DET 403 DET Energy Generation and Storage