Charging gives off hydrogen, which is lighter than air and explosive — so the room is ventilated from below, sparked from nowhere, and kept flameproof. Hydrogen rises, so ventilation inlets sit below battery level with exhaust high; the exhaust fan is independent of other systems and its motor sits outside the gas passage with seals. Fan blades are non-sparking and outlet ducts corrosion-resistant; the fan must change the room air completely in not more than two minutes. No naked lights or smoking, no metal jugs for distilled water, flameproof lighting only, and emergency switchboards kept clear of the battery space. Where ventilation is sized for low-hydrogen batteries, a warning notice to that effect is posted visibly in the room. Surveyor follow-up: the exhaust fan has failed with batteries on charge — what do you do before entering the room?

A lead-acid cell gives 2 volts from lead plates in sulphuric acid; state of charge is read by specific gravity with a hydrometer, topped with distilled water only. Charge scale on a 12-V battery: about 12.75 V and SG 1.250 fully charged, falling to about 11.65 V and SG 1.100 fully flat. Hydrometer weekly: never test within half an hour of charging — let cells stabilise — read at eye level ignoring the meniscus, correct for temperature, rinse the tester after. Maintenance is simple routine: electrolyte level, clean tight terminals, secure casing, ventilation clear — suspicion of a weak cell earns a load test (typically 275 A across the terminals). Top up with distilled water only, never acid; keep charging clear of sparks and the battery room ventilated for hydrogen. Surveyor follow-up: one cell reads 1.100 while the rest read 1.240 — charge the bank or renew the cell, and why?

Battery rooms are checked dry, tight and ventilated: tops clean, terminals greased, electrolyte correct, charger healthy, air moving. Room dry and ventilated, exhaust fan and ducts proved — hydrogen rises, so inlets low and outlets high. Tops clean and dry, terminal nuts tight with petroleum jelly against corrosion, charger free of dirt and overheating. Electrolyte at level with correct specific gravity on the hydrometer; rubber gloves and goggles for any handling, never metal jugs. Indicators, alarms and changeover proved; emergency switchboard kept clear of the battery space. Surveyor follow-up: one cell gassing hard with the rest quiet — charge the bank or pull the cell?

Battery room entring precautions

Battery rooms hide hydrogen: ventilate first, kill ignition sources, wear protection and never trust your nose. Ventilate before entering — hydrogen is lighter than air and peaks during charging or with fans stopped. No naked lights, smoking, sparking tools or metal jugs; flameproof lights only with notices posted. Fan blades non-sparking with the motor outside the gas stream, ducts corrosion-proof, inlets below battery level. Rubber gloves and goggles for electrolyte, petroleum jelly on terminals, hydrometer readings logged before leaving. Surveyor follow-up: exhaust fan dead with batteries gassing — enter now or wait, and what do you do first?

Battery specific gravity

Specific gravity is the battery’s fuel gauge: about 1.27–1.285 full, 1.10–1.09 flat, read weekly on a rested cell. Fully charged reads near 1.25 at 12.75 volts; each 10% of discharge drops gravity about 0.015 and volts about 0.1. Flat lands near 1.10 at 11.65 volts — charge at once, never leave her standing discharged. Test weekly with a temperature-corrected hydrometer, half an hour after charge or discharge, rinsed after. One cell far below its neighbours means a sick cell, not a flat bank — load-test it before condemning all. Surveyor follow-up: all cells 1.16 with the charger showing float — charged, discharged or sulphated?

Battery room regulation

Battery rooms obey ventilation and ignition rules: hydrogen out the top, sparks never in, flameproof fittings throughout. Ventilate so lighter-than-air hydrogen cannot gather — outlets high, inlets below battery level, fans independent. Fan blades spark-proof with motors outside the gas stream; ducts corrosion-proof and weather-guarded. No naked lights, smoking, metal jugs or switchboards inside; flameproof lights with posted warnings. Shorting tools across terminals arcs even ventilated — insulate, isolate and cover before working. Surveyor follow-up: exhaust fan dead with batteries gassing — enter now or wait, and what first?

Battery rounds check charge, connections and room: volts, gravity, terminals, charger and ventilation every watch. Read volts and specific gravity per cell against the maker table with temperature noted. Terminals tight, greased and corrosion-free with glands, trays and hold-downs sound. Charger proved on float and boost with alarms for failure and earth fault. Room ventilated, dry and hydrogen-free with lights flameproof and metal jugs banned. Surveyor follow-up: one cell flat with the rest full — charge the bank or renew the cell, and why?

Type of emergency battery

Emergency batteries are lead-acid for cheap bulk or nickel-cadmium for rugged memory-free standby — voltage per cell decides the count. Lead-acid gives 2 volts per cell with dilute sulphuric acid — cheap, heavy, sulphation-prone, fast to fade. Nickel-cadmium gives 1.2 volts per cell on potassium hydroxide — dear, tough, heat-tolerant, long self-discharge. Lead needs more maintenance and true hydrometer rounds; NiCd needs fewer tops with longer standby patience. GMDSS, alarms and lighting each name their chemistry on the battery certificate — fit what the approval states. Surveyor follow-up: 24-volt bank needed — how many cells lead versus NiCd, and what changes in the charger?

The collision bulkhead seals the bow: not too far forward to crush at once, not too far aft to flood deep. Foremost bulkhead bounding the forepeak against bow damage. Positioned by rule between minimum and maximum distances from the forward perpendicular by length. No doors, manholes or ducts pierce it except tightly controlled piped penetrations. One flooded bow compartment survivable — progressive flooding aft never allowed. Surveyor follow-up: pipe through the collision bulkhead with valves both sides — allowed or not?

Emergency power requirement

Emergency power rides a generator or battery with auto changeover: 45-second start, 18-hour transitional cover, dead-ship recovery inside 30 minutes. Generator or battery source with independent fuel at 43 degrees flash point and up. Auto-start on mains failure with auto-connection to the emergency board inside 45 seconds. Transitional batteries hold voltage inside 12% while carrying lights and services across the gap. Dead-ship services recover inside 30 minutes after blackout with emergency board near its source. Surveyor follow-up: emergency board dead with the set running — changeover, breaker or battery, and where first?

Batteries & Emergency Power — Most Asked Questions

23 questions asked about batteries & emergency power across the General and Fn 5 and Fn 4b papers, heaviest first. 2 of them are must-master.

Learn the system first

Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution The Emergency Generator — Location, Starting, Fuel and the Emergency Board Emergency Generator: Testing & Requirements

23 questions 0 ticked

1 Battery Room Safety?

Must master Theory asked 38 times · across 8 examiner banks General
Answer

Charging gives off hydrogen, which is lighter than air and explosive — so the room is ventilated from below, sparked from nowhere, and kept flameproof.
- Hydrogen rises, so ventilation inlets sit below battery level with exhaust high; the exhaust fan is independent of other systems and its motor sits outside the gas passage with seals.
- Fan blades are non-sparking and outlet ducts corrosion-resistant; the fan must change the room air completely in not more than two minutes.
- No naked lights or smoking, no metal jugs for distilled water, flameproof lighting only, and emergency switchboards kept clear of the battery space.
- Where ventilation is sized for low-hydrogen batteries, a warning notice to that effect is posted visibly in the room.
Surveyor follow-up: the exhaust fan has failed with batteries on charge — what do you do before entering the room?
Full theory: Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution
2 Lead acid battery

Must master Theory asked 16 times · across 9 examiner banks General
Answer

A lead-acid cell gives 2 volts from lead plates in sulphuric acid; state of charge is read by specific gravity with a hydrometer, topped with distilled water only.
- Charge scale on a 12-V battery: about 12.75 V and SG 1.250 fully charged, falling to about 11.65 V and SG 1.100 fully flat.
- Hydrometer weekly: never test within half an hour of charging — let cells stabilise — read at eye level ignoring the meniscus, correct for temperature, rinse the tester after.
- Maintenance is simple routine: electrolyte level, clean tight terminals, secure casing, ventilation clear — suspicion of a weak cell earns a load test (typically 275 A across the terminals).
- Top up with distilled water only, never acid; keep charging clear of sparks and the battery room ventilated for hydrogen.
Surveyor follow-up: one cell reads 1.100 while the rest read 1.240 — charge the bank or renew the cell, and why?
Full theory: Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution
3 Battery room checks

High priority Theory asked 7 times · across 6 examiner banks · 4 wordings merged General

Also asked: “Battery room checks prior entry”, “After entering battery room what checks you will do”, “batterey room what all to check”
Answer

Battery rooms are checked dry, tight and ventilated: tops clean, terminals greased, electrolyte correct, charger healthy, air moving.
- Room dry and ventilated, exhaust fan and ducts proved — hydrogen rises, so inlets low and outlets high.
- Tops clean and dry, terminal nuts tight with petroleum jelly against corrosion, charger free of dirt and overheating.
- Electrolyte at level with correct specific gravity on the hydrometer; rubber gloves and goggles for any handling, never metal jugs.
- Indicators, alarms and changeover proved; emergency switchboard kept clear of the battery space.
Surveyor follow-up: one cell gassing hard with the rest quiet — charge the bank or pull the cell?
Full theory: Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution
4 Battery room entring precautions

High priority Theory asked 6 times · across 5 examiner banks · 4 wordings merged General

Also asked: “Saftey to be taken when going in battery room”, “Precaution to enter battery room”, “Battery room entrance precaution”
Answer

Battery rooms hide hydrogen: ventilate first, kill ignition sources, wear protection and never trust your nose.
- Ventilate before entering — hydrogen is lighter than air and peaks during charging or with fans stopped.
- No naked lights, smoking, sparking tools or metal jugs; flameproof lights only with notices posted.
- Fan blades non-sparking with the motor outside the gas stream, ducts corrosion-proof, inlets below battery level.
- Rubber gloves and goggles for electrolyte, petroleum jelly on terminals, hydrometer readings logged before leaving.
Surveyor follow-up: exhaust fan dead with batteries gassing — enter now or wait, and what do you do first?
Full theory: Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution
5 Battery specific gravity

Revise Theory asked 6 times · across 3 examiner banks · 2 wordings merged General

Also asked: “Specific gravity of battery when it get discharged”
Answer

Specific gravity is the battery’s fuel gauge: about 1.27–1.285 full, 1.10–1.09 flat, read weekly on a rested cell.
- Fully charged reads near 1.25 at 12.75 volts; each 10% of discharge drops gravity about 0.015 and volts about 0.1.
- Flat lands near 1.10 at 11.65 volts — charge at once, never leave her standing discharged.
- Test weekly with a temperature-corrected hydrometer, half an hour after charge or discharge, rinsed after.
- One cell far below its neighbours means a sick cell, not a flat bank — load-test it before condemning all.
Surveyor follow-up: all cells 1.16 with the charger showing float — charged, discharged or sulphated?
Full theory: Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution
6 Battery room regulation

Revise Theory asked 5 times · across 3 examiner banks General
Answer

Battery rooms obey ventilation and ignition rules: hydrogen out the top, sparks never in, flameproof fittings throughout.
- Ventilate so lighter-than-air hydrogen cannot gather — outlets high, inlets below battery level, fans independent.
- Fan blades spark-proof with motors outside the gas stream; ducts corrosion-proof and weather-guarded.
- No naked lights, smoking, metal jugs or switchboards inside; flameproof lights with posted warnings.
- Shorting tools across terminals arcs even ventilated — insulate, isolate and cover before working.
Surveyor follow-up: exhaust fan dead with batteries gassing — enter now or wait, and what first?
Full theory: Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution
7 Checks on battery

Revise Theory asked 4 times · across 3 examiner banks · 2 wordings merged General

Also asked: “check made on battery”
Answer

Battery rounds check charge, connections and room: volts, gravity, terminals, charger and ventilation every watch.
- Read volts and specific gravity per cell against the maker table with temperature noted.
- Terminals tight, greased and corrosion-free with glands, trays and hold-downs sound.
- Charger proved on float and boost with alarms for failure and earth fault.
- Room ventilated, dry and hydrogen-free with lights flameproof and metal jugs banned.
Surveyor follow-up: one cell flat with the rest full — charge the bank or renew the cell, and why?
Full theory: Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution
8 Type of emergency battery

Revise Theory asked 4 times · across 3 examiner banks · 2 wordings merged General

Also asked: “Types of battery”
Answer

Emergency batteries are lead-acid for cheap bulk or nickel-cadmium for rugged memory-free standby — voltage per cell decides the count.
- Lead-acid gives 2 volts per cell with dilute sulphuric acid — cheap, heavy, sulphation-prone, fast to fade.
- Nickel-cadmium gives 1.2 volts per cell on potassium hydroxide — dear, tough, heat-tolerant, long self-discharge.
- Lead needs more maintenance and true hydrometer rounds; NiCd needs fewer tops with longer standby patience.
- GMDSS, alarms and lighting each name their chemistry on the battery certificate — fit what the approval states.
Surveyor follow-up: 24-volt bank needed — how many cells lead versus NiCd, and what changes in the charger?
Full theory: Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution
9 Collision bulk head

Revise Theory asked 3 times · across 3 examiner banks Fn 5
Answer

The collision bulkhead seals the bow: not too far forward to crush at once, not too far aft to flood deep.
- Foremost bulkhead bounding the forepeak against bow damage.
- Positioned by rule between minimum and maximum distances from the forward perpendicular by length.
- No doors, manholes or ducts pierce it except tightly controlled piped penetrations.
- One flooded bow compartment survivable — progressive flooding aft never allowed.
Surveyor follow-up: pipe through the collision bulkhead with valves both sides — allowed or not?
Full theory: Ship Bulkheads: Watertight, Corrugated and Fire
10 Emergency power requirement

Revise Theory asked 3 times · across 3 examiner banks General
Answer

Emergency power rides a generator or battery with auto changeover: 45-second start, 18-hour transitional cover, dead-ship recovery inside 30 minutes.
- Generator or battery source with independent fuel at 43 degrees flash point and up.
- Auto-start on mains failure with auto-connection to the emergency board inside 45 seconds.
- Transitional batteries hold voltage inside 12% while carrying lights and services across the gap.
- Dead-ship services recover inside 30 minutes after blackout with emergency board near its source.
Surveyor follow-up: emergency board dead with the set running — changeover, breaker or battery, and where first?
Full theory: Emergency Generator: Testing & Requirements
11 Light safety in battery room (explosion proof

Revise Theory asked 3 times · across 3 examiner banks · 2 wordings merged General

Also asked: “Lighting in battery room Winch safety”
Answer

Battery rooms burn on hydrogen: ventilate high, light flameproof, ban every spark source inside.
- Hydrogen sixteen times lighter than oxygen gathers at the top — outlets high, inlets below battery level.
- Flameproof lights only with posted no-smoking and no-naked-light notices backed by verbal warnings.
- Exhaust fans independent with spark-proof blades and motors sealed outside the gas stream.
- Emergency boards, metal jugs and sparking tools stay outside — gas peaks on charge or dead ventilation.
Surveyor follow-up: exhaust fan dead with batteries gassing — enter now or wait, and what first?
Full theory: Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution
12 Types of battery used onboard?

Revise Your ship asked 3 times · across 3 examiner banks General
Answer

Ships sail lead-acid for cheap bulk and nickel-cadmium for rugged standby: 2 volts against 1.2 volts per cell.
- Lead-acid on dilute sulphuric acid — cheap, heavy, sulphation-prone, fast to fade, thirsty for maintenance.
- Nickel-cadmium on potassium hydroxide — dear, tough, heat-tolerant, long self-discharge, no sulphation.
- Capacities rate in ampere-hours with liquid thermometers only — mercury near batteries sparks disaster.
- Electrolytes never swap: acid poured to water for lead, potash for NiCd, each to its own recipe.
Surveyor follow-up: 24-volt bank needed — how many cells lead versus NiCd, and what changes in the charger?
Full theory: Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution
13 Capacity of battery

Revise Theory asked 3 times · across 2 examiner banks General
Answer

Battery capacity is ampere-hours at a stated rate: faster discharge, colder cells and older plates all shrink it.
- Rated by constant-current discharge to terminal voltage near 1.75 V per cell, usually at 25°C.
- UK quotes the 10-hour rate, the US the 8-hour, with 20-hour figures safest for comparison.
- Capacity falls as discharge rate rises, temperature drops and sulphation or shedding ages the plates.
- Size emergency banks by load and duty time with margins — the surveyor reads the discharge tables, not the label.
Surveyor follow-up: bank rated 200 Ah at 10 hours dying in 6 on load — rate, temperature or age, and what test proves it?
Full theory: Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution
14 turbo charger surging reasons

Revise Fault finding asked 3 times · across 2 examiner banks · 2 wordings merged Fn 4b

Also asked: “What is turbo charger surging? Why it happens?”
Answer

Surging is the compressor stalling and banging: fouled gas and air paths, sudden load swings or fuel starvation unbalance the flow.
- Fouled filters, blower, turbine, nozzle ring and economiser choke mass flow until the blades stall.
- Manoeuvring, rough seas, overload and crash-astern swings plus rpm hunting shake the flow balance.
- Fuel starvation from dirty filters, faulty pumps and wrong timing starves gas energy to the turbine.
- Cure by slowing to drop scavenge pressure, then cleaning the path and steadying load before winding back up.
Surveyor follow-up: surging with filters clean and load steady but exhaust temperatures split — fuel, timing or turbine fouling first?
Full theory: Marine Turbochargers: Aerodynamics, Bearings, Washing & Surge Mitigation
15 Battery and battery room maintenence

Revise Theory asked 2 times · across 2 examiner banks · 2 wordings merged General

Also asked: “Battery roomm safety and maintenanace”
Answer

Battery care is measurement and cleanliness: specific gravity, level, terminals, room temperature and ventilation, all logged.
- Check the charging circuit, keep the battery top clean and dry, and keep terminal nuts tight with petroleum jelly against corrosion.
- Check electrolyte level and specific gravity with a hydrometer, and record the reading against the cell rather than the bank.
- Keep the room dry, insulated and between about 15 and 25 degrees, with ventilation running continuously.
- Check the charging equipment for dirt, overheating and loose connections, and avoid excessive rapid charging.
Surveyor follow-up: room at 30 degrees with the fan on and the readings falling — is the charger, the cells or the cooling first?
Full theory: Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution
16 Battery room safety whatbis dead front pannel and how it work

Revise Theory asked 2 times · across 2 examiner banks General
Answer

A battery room is a dead-front, flameproof space: all live parts behind steel, only the switch handle showing on the face.
- Dead-front means no live conductor is exposed — everything sits behind steel cubicles with handles and instruments forward.
- Lighting must be flameproof, and naked lights and smoking are restricted because hydrogen collects under the canopy.
- Emergency switchboards are kept away from the battery space, and metal jugs are banned as distilled water containers.
- Tools and portable lamps must be explosion-proof, and rubber apron and gloves protect against the electrolyte.
Surveyor follow-up: battery room with an ordinary bulkhead lamp and a naked light holder — how many findings does the surveyor raise?
Full theory: Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution
17 Gasses produce in battery room

Revise Theory asked 2 times · across 2 examiner banks General
Answer

Charging a lead-acid battery makes hydrogen, and on overcharge hydrogen and oxygen together make an explosive mixture.
- Electrolyte is sulphuric acid, and charging gases it — hydrogen on the negative side, oxygen on the positive.
- Hydrogen is lighter than air and collects under the canopy, so ventilation inlets go below battery level.
- Exhaust fan blades must be non-sparking, with the motor outside the duct and sealed against gas entry.
- The fan runs continuously and independently of other ventilation, with corrosion-resistant outlet ducts.
Surveyor follow-up: hydrogen alarm in a battery room with the exhaust fan running on the ship’s normal ventilation — isolated or shared?
Full theory: Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution
18 M/E is battery/Air staring. Engine is not getting started, what could be the problems

Revise Fault finding asked 2 times · across 2 examiner banks General
Answer

A battery start that will not crank is air, charge or a jammed engine — check in that order and never crank indefinitely.
- Battery: check the charge, the terminals for corrosion, the cells for a short, and the capacity against the cranking demand.
- Air: a stopped air compressor, empty receiver, leaking charge air or a closed control valve means no starting air at all.
- Engine: bar it over — a jammed engine or water in the cylinders will not move however good the air is.
- Starting air cannot be replenished while the engine is turning; bar first if there is any doubt, then investigate.
Surveyor follow-up: battery full, receiver at full pressure and the engine still not moving — what is left to check first?
Full theory: Starting the Engine — Air Start Valve, Distributor and the Four Interlocks
19 Maintenance of battery

Revise Theory asked 2 times · across 2 examiner banks · 2 wordings merged General

Also asked: “maintenance on Emergency battery”
Answer

Emergency battery maintenance follows the charge: terminals, electrolyte level, specific gravity and the cleanliness of the top.
- Keep terminals tight and coated, because corrosion there is the commonest cause of a set that will not carry load.
- Top up with distilled water to the maker’s mark — never acid, and never above the plates.
- Read specific gravity per cell to judge state of charge, and adjust the float charge to hold it full.
- Keep the battery on float, since a set left idle discharges itself and needs a boost before it will carry the emergency load.
Surveyor follow-up: emergency set at low specific gravity after a month alongside with no load — float setting or cells?
Full theory: Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution
20 Sketch and describe an arrangement for automatic connection of emergency batteries

Revise Sketch / drawing asked 2 times · across 2 examiner banks General
Answer

The emergency set connects automatically: contactors close on loss of supply so the emergency busbar is live without waiting for anyone.
- Emergency batteries sit on an emergency busbar fed through a normally-open contactor or a changeover switch.
- On failure of the normal supply the contactor energises from the battery and closes, taking the load with no delay.
- A charging arrangement keeps the batteries at float charge, with a supply to the emergency busbar from the emergency generator.
- The arrangement is drawn as source, contactor, busbar and consumers — and proved by cutting the normal supply in the drill.
Surveyor follow-up: emergency busbar dead on blackout with the battery full — contactor, control supply or charger first?
Full theory: Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution
21 Types of charging a battery?

Revise Theory asked 2 times · across 2 examiner banks General
Answer

Charging rates run float, boost and trickle: float holds a full battery, boost restores one quickly, trickle is the smallest maintenance feed.
- Float charge holds a fully charged battery against self-discharge with a very small continuous current.
- Boost charge restores capacity fast after a discharge, at a higher rate and with more heat and gas.
- Trickle charge is the low current used where the battery is not otherwise worked, and simply tops it up.
- Most modern chargers are single-rate, two-rate or smart units that select the rate themselves.
Surveyor follow-up: battery warm and gassing on float charge with the cell readings low — is it the charger rate or a weak cell?
Full theory: Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution
22 What if one cell in battery is defective

Revise Theory asked 2 times · across 2 examiner banks General
Answer

One weak cell holds the whole bank back: the charger works against it, the bank never reaches full charge and the cell may go short.
- A cell with high internal resistance or a short circuit draws current on charge and keeps the bank voltage down.
- On discharge that cell sags first, so the bank voltage collapses before the remaining cells are used up.
- Test each cell individually with the discharge tester, and compare specific gravity cell by cell rather than across the bank.
- Replace or recondition the cell — never leave a defective cell in an emergency battery, because the load fails on it.
Surveyor follow-up: one cell reading low with the bank at full voltage — is it the cell, the charger or the test itself?
Full theory: Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution
23 What is the specific gravity of electrolyte used in lead acid battery? 1280 at full charge and 1180 at discharge

Revise Theory asked 2 times · across 2 examiner banks · 2 wordings merged Fn 5

Also asked: “What should be the specific gravity of electrolyte of battery when fully charged discharged?”
Answer

Lead-acid electrolyte runs near 1.280 specific gravity fully charged and falls to about 1.180 at the end of discharge — that drop is the state of charge.
- A fully charged cell sits around 1.27 to 1.285; the 1.280 figure is the working value quoted on board.
- It falls to roughly 1.180 at end of discharge, and the battery is discarded or renewed near 1.110.
- State of charge is read per cell with a hydrometer, because one weak cell is invisible in a bank reading.
- Cells overcharged show higher specific gravity, undercharged lower, and an undercharged positive plate goes pale and hard to restore.
Surveyor follow-up: bank reading normal with one cell at 1.120 — is the bank charged, or is that cell the whole answer?
Full theory: Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution

Source: 123 written papers and surveyor oral banks, 24,613 entries, merged into 17,210 topics. Ticks are stored on this device only.