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NEETS Module 1 — Chapter 2

Batteries  ·  NAVEDTRA 14173

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Chapter 2: Batteries

Electrochemical action, primary and secondary cells, battery construction, maintenance, charging procedures, and safety — the direct-current power sources that keep Navy systems running.

📚 Source: NEETS Module 1
⏱ Est. Time: 60–75 minutes
🎯 Pass Score: 80%
📝 Final Questions: 20

🎓 LEARNING OBJECTIVES

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. 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

The POSITIVE electrode of a cell. In a lead-acid cell, the anode is lead peroxide.

Cathode

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

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 (SO₄) — these combine with zinc, eating it away (forming zinc sulfate). Excess electrons at carbon attract positive hydrogen ions (H₂) from the sulfuric acid. 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). Cell is fully restored.

🧪 Section 1 Knowledge Check

1. A cell is best described as a device that:

2. In a cell, the POSITIVE electrode is called the:

✅ Section 1 Complete!
2

Polarization, Local Action & Primary Cells

Polarization

Hydrogen bubbles accumulate on the anode surface 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: hydrogen not available for recharging)
  • 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.

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 most popular primary cell. 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 space program and miniaturized equipment.

⚠ 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 — ~2V; higher output capacity over longer time; disadvantage: produces hydrogen during operation
  • Lithium-Organic / Lithium-Inorganic — Very high power, wide temp range, lightweight, shelf life up to 20 years; contain toxic materials under pressure — do not puncture, recharge, or incinerate

🧪 Section 2 Knowledge Check

1. Polarization in a cell is caused by:

2. Local action in a cell is prevented by:

✅ Section 2 Complete!
3

Secondary Wet Cells

Secondary cells — also called wet cells — can be recharged by passing current through them in the direction opposite to discharge. There are four basic types.

🔋 Lead-Acid
Anode:Lead peroxide (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:Superior to lead-acid; 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 any number of times without appreciable damage
  • 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.

🧪 Section 3 Knowledge Check

1. Which secondary cell is most commonly used for EMERGENCY equipment?

2. Which three secondary cells share the same electrolyte (potassium hydroxide and water)?

✅ Section 3 Complete!
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 CURRENT, 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.

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

1. Four cells, each rated 1.5V and 1/8A, are connected in SERIES. What is the output voltage?

2. The type of a storage battery is most easily determined by:

✅ Section 4 Complete!
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.

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
  • Compare reading to 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 command-specific maintenance 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; notify medical department immediately

CAPACITY AND RATING

Capacity is measured in ampere-hours — the product of current (amperes) × time (hours). Ampere-hour capacity varies inversely with discharge current. Example: a 400 Ah battery delivers 400A for 1 hour OR 100A for 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 20-hour rate reduces available capacity.

🧪 Section 5 Knowledge Check

1. When electrolyte is splashed into the eyes, the FIRST action should be to:

2. A 200 ampere-hour battery is rated at the 20-hour discharge rate. How long can it deliver 10 amperes?

✅ Section 5 Complete!
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 specific gravity of all cells shows no change for 4 hours.

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

⚠ 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

1. Which type of battery charge is used to keep a battery at full charge while idle, using low current?

2. Violent gassing when a battery is FIRST placed on charge indicates:

✅ Section 6 Complete!

📋 Final Assessment

Answer all 20 questions, then click Submit. A score of 80% (16/20) or higher is required to pass.

1. A cell is a device that:

2. What are the three parts of a cell?

3. The POSITIVE electrode of a cell is called the:

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

5. In a carbon-zinc primary cell, what causes the negative (zinc) electrode to be eaten away?

6. Polarization of a cell causes:

7. Which method uses manganese dioxide to prevent polarization?

8. Local action in a cell is caused by:

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

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

11. The four basic types of secondary (wet) cells are:

12. In the lead-acid secondary cell, what materials make up the anode and cathode?

13. Which secondary cell is used extensively in AIRCRAFT storage batteries due to its high discharge rate capability?

14. Cells connected in PARALLEL provide:

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

16. Specific gravity is measured using a:

17. A 400 ampere-hour battery is discharged at 100 amperes. How long will it last?

18. Which type of battery charge is a special extended normal charge given periodically to drive all sulfate from the plates?

19. Can a discharged battery be recharged simply by adding more active ingredient to the electrolyte?

20. Steady gassing during battery charging indicates:

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NEETS Module 1 — Chapter 2
Batteries
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