Battery Technology & Energy Storage Flashcards

A technician performing a battery health check finds the pack capacity is 74% of original. Under US EPA and typical warranty standards, what does this usually indicate?

Answer: The battery is at or near the warranty replacement threshold, typically set at 70–80%

Most EV manufacturers set battery warranty replacement thresholds between 70–80% of original capacity, so 74% is at or near that threshold and warrants further inspection.

What role does the cathode material play in determining a lithium-ion battery's nominal voltage?

Answer: The electrochemical potential difference between cathode and anode materials sets the cell voltage

Cell voltage is determined by the difference in electrochemical potential (Gibbs free energy) between cathode and anode materials; different cathode chemistries produce different nominal voltages.

When storing an EV battery pack long-term, what state of charge (SOC) is recommended to minimize degradation?

Answer: Approximately 25–50% SOC

Storing lithium-ion batteries at 25–50% SOC minimizes cathode and anode stress, reduces SEI growth rate, and slows calendar aging compared to storage at extremes.

Which failure mode is indicated when a lithium-ion cell shows high self-discharge rate without mechanical damage?

Answer: Separator integrity loss or internal micro-short circuit

A high self-discharge rate without visible damage typically indicates micro-short circuits caused by lithium dendrites or separator degradation allowing electron leakage between electrodes.

How does regenerative braking affect the state of charge and temperature of an EV battery pack?

Answer: It charges the battery and may increase temperature due to charge current

Regenerative braking converts kinetic energy into electrical energy, increasing battery SOC while also generating heat due to charging current flowing through the pack's internal resistance.

What is the primary difference between 'calendar aging' and 'cycle aging' in battery degradation?

Answer: Calendar aging is time and temperature-dependent degradation at rest; cycle aging results from repeated charge/discharge use

Calendar aging degrades the battery simply by sitting over time (accelerated by heat and high SOC), while cycle aging accumulates damage through the mechanical and chemical stresses of charging and discharging.

An EV's BMS activates a 'high voltage interlock loop' (HVIL) fault and disconnects the pack contactors. What does this indicate?

Answer: A break in the high-voltage connector safety loop has been detected, indicating an open circuit or connector issue

The HVIL is a series safety circuit through HV connectors; a fault means the loop is broken, indicating an open HV connector, damaged wiring, or a cover removed from a HV component.