Title: Module 6: Battery Failure & Diagnosis - Quiz
Course: ASE A6 Battery Service > Section: Module 6: Battery Failure & Diagnosis

Q: The most common cause of battery sulfation is:
- Overcharging at high voltage
- Chronic undercharging
- Using the wrong electrolyte
- Excessive vibration
A: Chronic undercharging
Feedback: Chronic undercharging leaves lead sulfate on the plates that never fully converts back to active material. Over time, this soft sulfate hardens into crystals that permanently reduce battery capacity. This is the most common real-world cause of sulfation.

Q: Technician A says sulfation can always be reversed with a slow charge. Technician B says hard, crystallized sulfation is usually permanent. Who is correct?
- Technician A only
- Technician B only
- Both Technician A and Technician B
- Neither Technician A nor Technician B
A: Technician B only
Feedback: Soft, early-stage sulfation can sometimes be reversed with a prolonged slow charge (24-72 hours at 2-5 amps). However, once the lead sulfate has crystallized into hard deposits, it is extremely resistant to conversion and the damage is usually permanent.

Q: A battery has an open-circuit voltage of 10.5V. What is the most likely cause?
- The battery is 50% discharged
- The alternator is overcharging
- One cell is internally shorted
- All six cells are equally weak
A: One cell is internally shorted
Feedback: A fully charged battery reads 12.6V (six cells at 2.1V each). An OCV of 10.5V indicates that one cell has dropped to near 0V (5 cells x 2.1V = 10.5V). The most common cause is an internal short circuit from sediment bridging the plates within one cell.

Q: Plate shedding in a lead-acid battery results in:
- Electrolyte level rising above the plates
- Active material falling from the grids and accumulating as sediment
- The battery case expanding due to gas pressure
- Increased specific gravity in all cells
A: Active material falling from the grids and accumulating as sediment
Feedback: Plate shedding occurs when the active material (paste) physically separates from the plate grid lattice and falls to the bottom of the cell as sediment. This reduces the active plate surface area and can eventually cause internal short circuits if the sediment bridges the plates.

Q: The acceptable range for parasitic (key-off) battery draw on most vehicles is:
- 0-5 mA
- 25-50 mA
- 100-200 mA
- 500-1000 mA
A: 25-50 mA
Feedback: Most vehicles have a normal parasitic draw of 25-50 mA (0.025-0.050 amps) to maintain the clock, radio memory, body control module, and other systems requiring constant power. Draws above 85 mA are considered excessive and require diagnosis.

Q: When performing a parasitic draw test, why must you wait 20-60 minutes after turning the vehicle off before reading the meter?
- The battery needs time to develop surface charge
- The DMM needs time to calibrate
- Vehicle modules need time to enter sleep mode
- The alternator is still producing voltage
A: Vehicle modules need time to enter sleep mode
Feedback: Modern vehicles have numerous electronic modules (BCM, infotainment, seat modules, etc.) that remain active for 20-60 minutes after shutdown before entering low-power sleep mode. Testing before modules sleep will produce a falsely high reading that does not represent the actual resting parasitic draw.

Q: Technician A says the fuse-pulling method involves pulling all fuses at once to see the total draw reduction. Technician B says fuses should be pulled one at a time while monitoring the ammeter to identify which circuit has the excessive draw. Who is correct?
- Technician A only
- Technician B only
- Both Technician A and Technician B
- Neither Technician A nor Technician B
A: Technician B only
Feedback: The correct fuse-pulling method requires pulling fuses one at a time while watching the ammeter. When pulling a specific fuse causes the draw to drop to an acceptable level, that circuit contains the source of the excessive draw. Pulling all fuses at once provides no useful diagnostic information about which circuit is responsible.

Q: A battery date code reads "F4." This battery was manufactured in:
- February 2004
- June 2004
- February 2024
- June 2024
A: June 2024
Feedback: Battery date codes use a letter for the month (A=January through L=December) and a number for the last digit of the year. F is the 6th letter, representing June. The digit 4 represents 2024 (in the current decade context). So F4 = June 2024.

Q: Which of the following is the MOST likely cause of an aftermarket accessory creating a parasitic draw?
- The accessory was wired to a switched power source
- The accessory was wired directly to constant battery power
- The accessory fuse is too large
- The accessory ground wire is too short
A: The accessory was wired directly to constant battery power
Feedback: Aftermarket accessories (stereos, alarms, dash cameras, LED lights) that are wired directly to constant battery power will draw current even when the vehicle is off. Properly installed accessories should be wired to switched power so they turn off with the ignition. This is one of the most common causes of excessive parasitic draw.

Q: A vehicle's battery keeps dying overnight. The battery tests good on both load test and conductance test. The charging system output is within specification. What should the technician check next?
- Replace the battery — it must have an intermittent internal fault
- Replace the alternator — it is not charging properly
- Perform a parasitic draw test
- Add distilled water to the battery
A: Perform a parasitic draw test
Feedback: When the battery tests good and the charging system is within specification, the most likely cause of repeated overnight discharge is excessive parasitic draw. A parasitic draw test will measure the key-off current drain and determine if a circuit is drawing too much power while the vehicle is off.

Q: Technician A says batteries in hot climates typically last longer because heat prevents sulfation. Technician B says batteries in hot climates typically have shorter lifespans because heat accelerates plate corrosion and water loss. Who is correct?
- Technician A only
- Technician B only
- Both Technician A and Technician B
- Neither Technician A nor Technician B
A: Technician B only
Feedback: Heat is the primary enemy of battery longevity. High temperatures accelerate plate corrosion, increase water loss through evaporation and electrolysis, speed up paste degradation, and promote sulfation. Batteries in hot climates (southern states) typically last 3-4 years, while batteries in cold climates may last 4-6 years.

Q: A fully charged six-cell battery reads 12.6V. Individual cell voltage testing shows five cells at 2.12V and one cell at 1.96V. This indicates:
- A perfectly balanced battery
- Cell imbalance — the weak cell will limit battery performance
- The battery is overcharged
- The hydrometer is malfunctioning
A: Cell imbalance — the weak cell will limit battery performance
Feedback: A healthy, fully charged cell reads 2.10-2.15V. One cell reading 1.96V is noticeably weaker than the others, indicating cell imbalance. This weak cell will limit the battery's overall performance, especially under load, because the battery is only as strong as its weakest cell.

Q: During a parasitic draw test, the DMM should initially be set to:
- The milliamp (mA) scale for immediate accuracy
- The AC voltage scale
- The highest DC amperage scale (10A or 20A)
- The resistance (ohms) scale
A: The highest DC amperage scale (10A or 20A)
Feedback: The DMM should be set to the highest DC amperage scale first (10A or 20A) to protect the meter's milliamp fuse. If an unexpectedly high draw exists, it could blow the milliamp fuse or damage the meter. Once the reading is confirmed to be low, the technician switches to the milliamp scale for a more accurate measurement.

Q: A customer's vehicle has a 500 mA parasitic draw. Using the fuse-pulling method, the technician pulls the fuse labeled "Interior Lights" and the draw drops to 40 mA. Which of the following is the MOST likely cause?
- The alternator is overcharging
- A trunk or glove box light switch is faulty, keeping the light on
- The battery is sulfated
- The negative battery cable is corroded
A: A trunk or glove box light switch is faulty, keeping the light on
Feedback: When pulling the "Interior Lights" fuse caused the draw to drop from 500 mA to the acceptable 40 mA range, the excessive draw is on the interior light circuit. The most common cause is a faulty switch on a trunk light, glove box light, or underhood light that keeps the light on even when the compartment is closed.

Q: Which battery failure mode is caused by vibration and deep discharge cycling, and can result in an internal short circuit if enough material accumulates?
- Sulfation
- Electrolyte stratification
- Plate shedding
- Thermal runaway
A: Plate shedding
Feedback: Plate shedding is the physical separation of active material from the plate grids, caused by vibration, deep cycling, overcharging, and age. The shed material collects as sediment at the bottom of the cell. If sediment accumulates high enough to bridge the gap between positive and negative plates, it creates an internal short circuit.