Cells and Batteries

Which factor most reduces the life cycle of a lead-acid battery?

Over-discharging and sulfation

During discharge of a lead-acid battery, what compound forms on both positive and negative plates?

Lead sulfate (PbSO4)

What key safety hazard makes lithium-ion batteries different from other rechargeable batteries?

They contain flammable pressurized electrolyte

What advantage do SLA batteries provide regarding maintenance and testing?

They include built-in test circuits for easy evaluation in aircraft

Why should water only be added to Ni-Cad batteries when fully charged?

Electrolyte level rises with charge, preventing overfilling

In a typical dry cell, which component acts as the cathode?

Graphite rod or metal electrode

Why is the ampere-hour rating of a battery lower under heavy discharge conditions?

Heat buildup reduces efficiency and capacity

Why must hydrometer readings be taken before adding distilled water?

Added water may dilute the sample and mislead results

A hydrometer reading of 1.200 in an aircraft battery indicates:

Low state of charge requiring recharge

What determines the voltage of a battery?

The number of cells connected in series

What is the typical open circuit cell voltage of a Ni-Cad battery?

1.25 V

Why are lithium-ion batteries favored in modern aircraft like the Boeing 787?

They are lighter and provide higher power output

Why must the charging voltage for a lead-acid battery exceed the open circuit voltage?

To overcome electrolyte resistance and ensure current flow

What condition often misleads technicians into believing a Ni-Cad battery is fully charged?

Memory effect (voltage depression)

During charging of a Ni-Cad battery, why must slight gassing occur?

To complete full charge conversion of active materials

Which charging method poses a higher risk of overcharging if not carefully controlled?

Constant current method

The Boeing 787's lithium-ion battery configuration provides what key operational benefit?

It delivers up to 150 amps for airplane power-up

What is the primary reason aircraft batteries include a venting system connected to a sump jar?

To neutralize acidic gases before overboard discharge

What safety precaution is unique to Ni-Cad maintenance compared to lead-acid?

Neutralize spills with vinegar or boric acid solution

A 24V aircraft battery requires how many lead-acid cells in series?

12

Why are sealed lead-acid (SLA) batteries often preferred over Ni-Cad in standby applications?

They do not suffer from voltage depression or memory effect

What does a hydrometer measure in a lead-acid battery?

Electrolyte specific gravity

What failure risk occurs in Ni-Cad batteries during end-of-discharge if cells are unmatched?

Cell explosion due to reversal

Why is it dangerous to attempt recharging a primary cell?

The electrochemical reaction is not reversible and can cause explosion

Why do aircraft lead-acid batteries include porous separators between plates?

To allow electrolyte circulation and prevent shorting