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NEETS Module 1 — Chapter 2

Batteries  ·  NAVEDTRA 14173

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Chapter 2: Batteries

How cells turn chemical energy into electricity, how cells combine into batteries, and how to maintain, charge, and work safely around them.

Course Duration: 50–70 minutes

📚 Source: NEETS Module 1 (NAVEDTRA 14173)
🎯 Pass Score: 80% (16 of 20)
📝 Final Questions: 20

🎓 LEARNING OBJECTIVES

  • State the purpose of a cell and its three parts
  • Distinguish primary and secondary cells and their chemical action
  • Define electrochemical action, anode, cathode, and electrolyte — and know how NEETS terms differ from modern datasheets
  • Explain polarization and local action, their causes, and prevention
  • Identify primary dry cells and secondary cells and their characteristics
  • Explain series, parallel, and series-parallel cell connections
  • Describe battery maintenance: hydrometer use, capacity, and rating
  • Identify the five types of battery charge and observe battery safety precautions

🛈 HOW THIS COURSE WORKS

  • Six sections, each ending with a knowledge check. You get two attempts, and a first miss gives you a hint rather than the answer. Answering unlocks the next section.
  • Then a 20-question final assessment, different from the knowledge checks.
  • When you submit, your results are emailed automatically to the training administrator and to you, whether or not you pass.
1

The Cell: Structure & Electrochemical Action

A cell is a device that transforms chemical energy into electrical energy. The simplest cell — known as a galvanic or voltaic cell — consists of a carbon electrode and a zinc electrode suspended in a sulfuric-acid-and-water electrolyte (the NEETS example). A battery is a number of cells assembled in a common container.

⚡
Electrodes

The conductors by which current leaves or returns to the electrolyte. Carbon (positive) and zinc (negative) in a simple cell.

💧
Electrolyte

The solution that acts upon the electrodes. May be a salt, acid, or alkaline solution in liquid or paste form.

🧱
Container

Holds the electrolyte and mounts the electrodes. Must resist the electrolyte and may serve as an electrode itself.

Electrochemical Action

The process of converting chemical energy into electrical energy. When a load is connected, electrons flow from the cathode (negative), through the external circuit, to the anode (positive).

Anode

In NEETS terminology, the POSITIVE electrode of a cell. In a lead-acid cell, the anode is lead peroxide (today called lead dioxide, PbO₂).

Cathode

In NEETS terminology, the NEGATIVE electrode of a cell. In a lead-acid cell, the cathode is sponge lead.

⚠ TERMINOLOGY NOTE — ANODE & CATHODE

NEETS, like many older electronics texts, names electrodes by polarity: anode = positive, cathode = negative. Modern electrochemistry and battery datasheets name them by the reaction instead. During discharge, the anode is where oxidation happens — the NEGATIVE terminal (the zinc in a dry cell) — and the cathode is the POSITIVE terminal. The two conventions are opposite. This module uses the NEETS terms to match the source. In the field, go by the + and − markings.

PRIMARY CELL vs. SECONDARY CELL

  • Primary cell — Chemical action destroys one electrode (usually negative). Cannot be recharged; must be replaced. Example: flashlight battery.
  • Secondary cell — Chemical action alters both electrodes and electrolyte, but can be REVERSED by forcing current through the cell in the opposite direction. Example: automobile storage battery.

PRIMARY CELL CHEMISTRY (Carbon-Zinc)

When current flows: electrons leave the zinc cathode toward the load. Positive zinc charge attracts negative sulfate ions (SO₄²⁻) — these combine with zinc, eating it away (forming zinc sulfate). Excess electrons at carbon attract positive hydrogen ions (H⁺) from the sulfuric acid; they pick up electrons and form hydrogen gas at the carbon. (NEETS prints these as SO₄ and H₂.) The zinc gradually dissolves, eventually dropping the cell voltage to zero.

SECONDARY CELL CHEMISTRY (Lead-Acid)

Discharging: Sulfuric acid chemically changes both sponge-lead cathode and lead-peroxide anode to lead sulfate. Acid concentration drops. Charging: External current reverses the process — lead sulfate converts back to sponge lead (cathode), lead peroxide (anode), and sulfuric acid (electrolyte). Acid concentration rises again and the cell is restored.

🧪 Section 1 Knowledge Check

What happens to the electrolyte in a lead-acid cell as it discharges?

Attempts: 0/2
2

Polarization, Local Action & Primary Cells

Polarization

Hydrogen bubbles accumulate on the surface of the anode (the positive carbon electrode) during current flow, forming a barrier that increases internal resistance. This reduces output current and voltage. A heavily polarized cell has no useful output.

PREVENTING POLARIZATION (three methods)

  • Vent the cell — allows hydrogen to escape into air (disadvantage: the hydrogen isn’t available for recharging, which is why vented batteries need water added)
  • Add oxygen-rich material — manganese dioxide supplies free oxygen to combine with hydrogen, forming water
  • Add hydrogen-absorbing material — calcium absorbs hydrogen; releases it during charging
Local Action

Continuation of current flow within the cell when there is NO external load. Caused by impurities (iron, carbon, lead, arsenic) in the zinc electrode forming small internal cells. Gradually discharges the cell even when not in use.

PREVENTING LOCAL ACTION

Treat the zinc electrode with mercury — a process called amalgamating the zinc. Mercury is denser than impurities; impurities float to its surface and are removed. The mercury is not acted upon by the acid, so it continues to pull impurities from the zinc during use. This greatly increases the cell's shelf life.

Today: the 1996 federal Battery Act (Mercury-Containing and Rechargeable Battery Management Act) ended intentionally added mercury in most U.S. batteries. Modern zinc cells are mercury-free, except for small amounts that remain in some button cells.

Shelf life is the period a cell may be stored and still remain usable. Cells stored in cool/refrigerated spaces have greatly extended shelf life.

PRIMARY DRY CELL (Leclanché Cell)

The classic carbon-zinc dry cell — the most popular primary cell when NEETS was written (alkaline cells are more common today). Uses a paste electrolyte (not truly dry) — a mix of ammonium chloride, manganese dioxide, zinc chloride, powdered coke, ground carbon, graphite, and water. Components: zinc container (cathode), carbon rod center electrode (anode), paste electrolyte, blotting paper separator. Manganese dioxide reduces polarization; zinc chloride reduces local action.

MERCURY CELL (Mercuric-Oxide Zinc)

Developed in WWII. Advantages: long current delivery, long shelf life, stable output voltage, very small size. Made in three types: wound-anode, and two pressed-powder variants. Used in the space program and miniaturized equipment. Since the 1996 Battery Act, mercuric-oxide batteries are restricted in the U.S. to uses such as military and medical equipment, with manufacturer take-back required. Silver-oxide, zinc-air, and lithium cells have replaced them in most uses.

⚠ WARNING — MERCURY CELLS

DO NOT short the mercury cell. Shorted mercury cells have exploded with considerable force.

OTHER PRIMARY CELLS

  • Alkaline (Manganese Dioxide-Alkaline-Zinc) — 1.5V; better voltage stability, longer life and shelf life, wider temperature range than zinc-carbon
  • Magnesium-Manganese Dioxide — Higher output capacity over longer time; disadvantage: produces hydrogen during operation
  • Lithium-Organic / Lithium-Inorganic — High energy for their weight, wide temperature range, shelf life up to 20 years; contain toxic materials under pressure — do not puncture, recharge, or incinerate. (These are primary lithium cells. Rechargeable lithium-ion cells came after NEETS and are secondary cells.)

🧪 Section 2 Knowledge Check

Why do dry cells keep longer when stored in a cool or refrigerated space?

Attempts: 0/2
3

Secondary Wet Cells

Secondary cells can be recharged by passing current through them in the direction opposite to discharge. NEETS covers four basic types of secondary wet cells. Many modern secondary cells are sealed instead — valve-regulated lead-acid (VRLA: AGM or gel), nickel-metal hydride, and lithium-ion.

🔋 Lead-Acid
Anode:Lead peroxide / lead dioxide (PbO₂)
Cathode:Sponge lead (Pb)
Electrolyte:Sulfuric acid + water
Notes:Most widely used secondary cell. Individual cells NOT replaceable.
⚡ Nickel-Cadmium (NICAD)
Anode:Nickel hydroxide
Cathode:Cadmium hydroxide
Electrolyte:Potassium hydroxide + water
Notes:NEETS rates it better than lead-acid in several ways; higher power at high discharge rates; individual cells ARE replaceable; used in aircraft batteries.
🚨 Silver-Zinc
Anode:Silver oxide
Cathode:Zinc
Electrolyte:Potassium hydroxide + water
Notes:Used for emergency equipment. Expensive, fewer charge cycles, but light, small, and high capacity.
🔆 Silver-Cadmium
Anode:Silver oxide
Cathode:Cadmium hydroxide
Electrolyte:Potassium hydroxide + water
Notes:Combines better features of NICAD and silver-zinc. More than twice the shelf life of silver-zinc. Disadvantages: high cost, low voltage.

NICAD ADVANTAGES OVER LEAD-ACID

  • Charges in a shorter time
  • Delivers larger power at high discharge rates
  • Stays idle longer in any state of charge
  • Can be charged and discharged many times without appreciable damage (NEETS says “any number,” but real cells still wear out eventually)
  • Individual cells can be replaced (lead-acid cells cannot)

SHARED ELECTROLYTE: THREE CELLS

Nickel-cadmium, silver-zinc, and silver-cadmium all use the same electrolyte: potassium hydroxide and water.

IN THE FIELD — LOW-VOLTAGE SYSTEMS

  • Fire alarm and security panels, access-control power supplies, and small UPS units use sealed 12V lead-acid (VRLA/AGM) standby batteries.
  • NFPA 72 calls for fire alarm VRLA batteries to be marked with their manufacture date and replaced within 5 years of it. Check the edition your authority having jurisdiction (AHJ) enforces.
  • Never open a sealed battery or add water to it. Nickel-cadmium batteries contain cadmium, so recycle them rather than putting them in the trash.

🧪 Section 3 Knowledge Check

Which three secondary cells share the same electrolyte, potassium hydroxide and water?

Attempts: 0/2
4

Batteries: Combining Cells & Construction

A battery is a voltage source in a single container made from one or more cells. When a device requires more energy than one cell can provide, cells are interconnected in three ways:

➡️
Series

Negative of one cell to positive of next. Increases VOLTAGE, current stays the same. Example: 4 cells × 1.5V = 6V at same current.

⬇️
Parallel

All positives together, all negatives together. Increases the CURRENT the battery can supply (and its ampere-hour capacity); voltage stays the same. Example: 4 cells × 1/8A = 1/2A at same voltage.

🔀
Series-Parallel

Groups in series (for voltage) then those groups in parallel (for current). Increases BOTH voltage and current beyond a single cell.

⚠ SERIES CONNECTION CAUTION

When connecting cells in series, connect alternate terminals (− to +, − to +). Never connect the two remaining end terminals together — this shorts the battery, can rapidly discharge cells, and may cause certain cell types to explode. When combining cells, use cells of the same type, age, and state of charge.

LEAD-ACID BATTERY CONSTRUCTION

  • Container: Hard rubber, plastic, or chemical-resistant material; vented through vent plugs for gas escape
  • Plates: Interlaced positive (anode) and negative (cathode) plate groups connected by link connectors
  • Terminals: Positive terminal (+) is physically LARGER and sometimes red; negative terminal (−) is smaller
  • Cells: Connected in series internally; individual cells are NOT replaceable

NICAD BATTERY CONSTRUCTION

Similar to lead-acid construction except individual cells CAN be replaced. Battery type is most easily determined from the nameplate data.

🧪 Section 4 Knowledge Check

When connecting cells in series, what must you never do?

Attempts: 0/2
5

Battery Maintenance: Specific Gravity & Safety

Specific gravity is the ratio of the weight of a substance to the weight of an equal volume of pure water. Pure water has a specific gravity of 1.0. Any substance that floats is less than 1.0; any substance that sinks is greater than 1.0. Battery electrolyte active ingredients are heavier than water, so electrolyte has a specific gravity greater than 1.0. A fully charged lead-acid cell typically reads about 1.265–1.280. Always use the manufacturer’s figure, corrected for electrolyte temperature.

Hydrometer

A glass syringe with an internal calibrated float used to measure the specific gravity of battery electrolyte. A higher float position = higher specific gravity = more active ingredient = more charge. Flush with fresh water after each use. Must not be used for any other purpose.

USING THE HYDROMETER

  • Draw electrolyte in using the suction bulb — enough to make the float rise, but not into the bulb
  • Hold hydrometer vertically; read scale where electrolyte surface touches the float
  • Correct the reading for electrolyte temperature, then compare it to the manufacturer's specification to determine charge state
  • Higher specific gravity = more active ingredient = more charge remaining

ROUTINE BATTERY MAINTENANCE

  • Check terminals for cleanliness and good electrical connection
  • Inspect battery case for cleanliness and damage
  • Check electrolyte level — add distilled water if low
  • Follow the manufacturer’s and your company’s maintenance procedures (NEETS says “command” procedures)

⚠ BATTERY SAFETY PRECAUTIONS

  • NEVER short the terminals of a battery
  • Use carrying straps when transporting batteries
  • Wear rubber apron, rubber gloves, and face shield when working with batteries
  • NO smoking, electric sparks, or open flames near charging batteries
  • Prevent spilling electrolyte; dilute spills immediately with large amounts of water
  • If electrolyte contacts skin or eyes: flush with large quantities of fresh water for a MINIMUM of 15 minutes; get medical attention immediately. OSHA requires a quick-drench or eye-flushing facility wherever a worker’s eyes or body may be exposed to corrosive materials (29 CFR 1910.151(c)).

CAPACITY AND RATING

Capacity is measured in ampere-hours — the product of current (amperes) × time (hours). On paper, 400 Ah could mean 400A for 1 hour or 100A for 4 hours (NEETS uses this example). In practice, usable capacity falls as discharge current rises (Peukert’s law). A battery rated 400 Ah at the 20-hour rate delivers 20A for 20 hours, but at 100A it runs for noticeably less than 4 hours.

Rating is based on a 20-hour discharge rate for most batteries (aircraft batteries: 1-hour rate). A battery delivering 20A for 20 hours has a rating of 400 Ah. Discharging faster than the rated rate reduces available capacity, so size standby batteries with margin.

🧪 Section 5 Knowledge Check

Electrolyte splashes into a coworker's eyes. What do you do first?

Attempts: 0/2
6

Battery Charging: Five Types & Gassing

A charging current must be passed through a battery to recharge it. Adding active ingredient to the electrolyte alone does NOT recharge the battery — it only temporarily increases specific gravity without converting the plates back to active material.

1
INITIAL CHARGE

Given to a new battery shipped dry (uncharged plates). A long, low-rate charge per manufacturer's instructions. Required before the battery can be placed in service.

2
NORMAL CHARGE

A routine charge given per nameplate data during ordinary operation to restore the battery to its charged condition.

3
EQUALIZING CHARGE

A special extended normal charge given periodically as maintenance. Drives all sulfate from the plates and restores all cells to maximum specific gravity. Continued until the specific gravity of all cells, corrected for temperature, shows no change for a 4-hour period.

4
FLOATING CHARGE (Trickle Charge)

Charging rate is determined by battery voltage rather than a set current value. Uses low current to keep a fully charged battery at full charge while idle or under light duty.

5
FAST CHARGE

Used only in emergencies when the battery must be recharged in the shortest possible time. Starts at much higher rate than normal. May be harmful to the battery.

GASSING DURING CHARGING

Charging current breaks down water in the electrolyte: hydrogen releases at negative plates, oxygen at positive plates. Bubbles rise through electrolyte and collect at the top of the cell.

  • Violent gassing at start of charge → charging rate is TOO HIGH; reduce it
  • Steady gassing as charging proceeds → normal; indicates battery is nearing full charge
  • Sealed (VRLA) batteries recombine most of this gas internally and vent only when overcharged — use a charger set for the battery type

⚠ HYDROGEN GAS WARNING

A mixture of hydrogen and air can be DANGEROUSLY EXPLOSIVE. No smoking, electric sparks, or open flames should be permitted near charging batteries.

🧪 Section 6 Knowledge Check

Violent gassing starts as soon as a battery is placed on charge. What does that tell you?

Attempts: 0/2

📋 Final Assessment

Answer all 20 questions, then submit. A score of 80% (16/20) or higher is required to pass. These questions are different from the section knowledge checks.

1. A cell is a device that:

2. What are the three parts of a cell?

3. In NEETS terminology, the POSITIVE electrode of a cell is called the:

4. The main difference between a primary and a secondary cell is:

5. In a carbon-zinc primary cell, what eats away the zinc electrode?

6. Polarization of a cell causes:

7. How does manganese dioxide prevent polarization?

8. Local action in a cell is caused by:

9. Amalgamating the zinc electrode with mercury prevented local action by:

10. Which primary cell is known for a very stable output voltage, long current delivery, and long shelf life?

11. NEETS describes four basic types of secondary wet cells. They are:

12. In NEETS terms, what are the anode and cathode of a lead-acid cell?

13. Which secondary cell does NEETS say is used extensively in aircraft batteries because it delivers high power at high discharge rates?

14. Cells connected in PARALLEL provide:

15. The positive terminal of a lead-acid battery is identified by being:

16. The specific gravity of battery electrolyte is measured with a:

17. A battery is rated 400 ampere-hours at the 20-hour rate. What current can it supply continuously for 20 hours?

18. Which charge is a special extended normal charge, given periodically, that drives all sulfate from the plates?

19. A technician adds sulfuric acid to raise a discharged battery's specific gravity. Does this recharge the battery?

20. Steady gassing as a charge proceeds usually means:

Assessment Results

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Score: 0 / 0

Percentage: 0%

Status: —

Time in course: —