Question 495 of 1,020

Mobile Device Hardware Servicing →easyMultiple ChoiceObjective-mapped

Laptop Battery Not Charging: BMS Failure Diagnosis

This 220-1201 practice question tests your understanding of mobile device hardware servicing. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

A user reports that their laptop battery no longer charges and the system only runs when plugged in. You test the AC adapter and it outputs correct voltage. Inside the battery, which component is most likely failed?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

A
The lithium-ion cells have degraded.
Why wrong: Degraded cells would still show some charge or cause shorter runtime, not a complete failure to charge.
B
The battery management system (BMS) is faulty.
A failed BMS prevents the battery from communicating with the charger and accepting power, causing no charging.
C
The DC jack on the laptop is loose.
Why wrong: The DC jack issue would affect power to the whole system, but the system runs fine on AC adapter.
D
The laptop's motherboard charging circuit is damaged.
Why wrong: If the motherboard circuit were bad, the system wouldn't run on AC power either.

Full breakdown with real-world context →

Quick Answer

The answer is a faulty battery management system (BMS). When a laptop battery stops charging but the AC adapter is confirmed to output correct voltage, the BMS is the most likely failed component because it governs the charging logic and communication between the battery cells and the laptop. Even if the individual lithium-ion cells are healthy, a failed BMS will prevent the battery from accepting a charge or reporting its status, leaving the system to run only on AC power. On the CompTIA A+ Core 1 220-1201 exam, this scenario tests your understanding of battery charging circuitry and the BMS’s role as the “gatekeeper” for power flow. A common trap is to assume the cells themselves are dead, but the BMS failure is the root cause when the adapter is verified working. Remember the memory tip: “BMS blocks the charge” — if the adapter is good but the battery won’t charge, suspect the management system, not the cells.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The battery management system (BMS) is faulty.

The battery management system (BMS) is the circuit board inside the battery pack that controls charging, monitors cell voltage and temperature, and communicates with the laptop. Since the AC adapter outputs correct voltage and the laptop runs on AC power, the BMS is the most likely failed component because it can prevent charging even if the lithium-ion cells are healthy. A faulty BMS may stop communicating with the laptop's embedded controller, causing the system to treat the battery as absent or non-functional.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
The lithium-ion cells have degraded.
Why it's wrong here
Degraded cells would still show some charge or cause shorter runtime, not a complete failure to charge.
✓
The battery management system (BMS) is faulty.
Why this is correct
A failed BMS prevents the battery from communicating with the charger and accepting power, causing no charging.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The DC jack on the laptop is loose.
Why it's wrong here
The DC jack issue would affect power to the whole system, but the system runs fine on AC adapter.
✗
The laptop's motherboard charging circuit is damaged.
Why it's wrong here
If the motherboard circuit were bad, the system wouldn't run on AC power either.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The 220-1201 exam often tests the misconception that battery failure always means the cells are dead, but the trap here is that the BMS can fail independently and prevent charging while the cells remain functional, especially when the AC adapter and laptop power path are verified working.

Trap categories for this question

Command / output trap
Degraded cells would still show some charge or cause shorter runtime, not a complete failure to charge.

Detailed technical explanation

How to think about this question

The BMS uses a fuel gauge IC (e.g., Texas Instruments bq40z50 or similar) that communicates via SMBus (System Management Bus) with the laptop's embedded controller. When the BMS detects a fault condition such as over-discharge, over-temperature, or cell imbalance, it can permanently disable the charging FET to prevent safety hazards, a state known as 'permanent failure' or 'suicide mode.' In real-world scenarios, a BMS can also fail due to electrostatic discharge or firmware corruption, causing the battery to appear dead even with healthy cells.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

TExam Day Tips

Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A practitioner preparing for the 220-1201 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this 220-1201 question test?

Mobile Device Hardware Servicing — This question tests Mobile Device Hardware Servicing — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The battery management system (BMS) is faulty. — The battery management system (BMS) is the circuit board inside the battery pack that controls charging, monitors cell voltage and temperature, and communicates with the laptop. Since the AC adapter outputs correct voltage and the laptop runs on AC power, the BMS is the most likely failed component because it can prevent charging even if the lithium-ion cells are healthy. A faulty BMS may stop communicating with the laptop's embedded controller, causing the system to treat the battery as absent or non-functional.

What should I do if I get this 220-1201 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

About these practice questions

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Same concept, more angles

1 more ways this is tested on 220-1201

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. A customer complains that their laptop battery no longer holds a charge and the laptop only works when plugged in. The technician confirms the battery is removable. What is the most appropriate first step in servicing this issue?

easy

A.Update the battery driver in Device Manager.
B.Run a battery calibration utility from the manufacturer.
✓ C.Power off the laptop and remove the battery.
D.Replace the AC adapter to see if the charging circuit is faulty.

Why C: The correct first step is to power off the laptop and remove the battery. This ensures safety and prevents electrical shorts or damage during replacement. After removal, the technician can install a new battery.

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