220-1101 Mobile Devices Practice Question
A user reports that their smartphone (Android) turns off without warning when the battery indicator shows 15-20% remaining. The phone will not power back on until it is connected to a charger, at which point it shows a much lower battery percentage (e.g., 2%). The user has already performed a battery calibration procedure (draining fully and charging to 100% uninterrupted) but the problem persists. Which of the following is the MOST likely cause?
⚠ Common exam trap
CompTIA often tests the distinction between a software calibration issue and a hardware defect; the trap here is that candidates assume a calibration procedure always fixes battery reporting problems, but when it fails, the root cause is a physically degraded battery, not a software glitch.
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
✓
Defective battery
The battery is defective because it has lost its ability to accurately report its state of charge and maintain voltage under load. When the battery indicator shows 15-20%, the actual voltage has already dropped below the cutoff threshold, causing the phone to shut down. The calibration procedure failed because the battery's internal impedance has increased, preventing it from holding a proper charge.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Faulty charging port
Why it's wrong here
A faulty charging port typically causes issues with charging (e.g., no charging, intermittent charging) or connectivity. It would not cause the phone to shut down at a specific battery percentage and then show a lower percentage when plugged in.
- ✓
Defective battery
Why this is correct
A defective or aged battery can have increased internal resistance, causing the voltage to sag under load. The fuel gauge may still report 15-20%, but the actual voltage is too low to keep the phone running. Calibration cannot fix physical battery degradation, so replacement is needed.
- ✗
Operating system software bug
Why it's wrong here
While a software bug could indeed cause incorrect battery percentage reporting or trigger premature shutdowns, such bugs typically produce erratic behavior, appear after an OS update, or affect many devices simultaneously. Battery recalibration—clearing the battery stats cache or performing a full discharge/charge cycle—usually resolves software-induced reporting issues. Here, calibration did nothing, and the shutdowns recur at a consistent 15–20% regardless of software state, indicating that the problem is not a logical error but a physical inability to deliver voltage. Furthermore, the fact that the phone powers on immediately when plugged in points to hardware-level voltage collapse rather than a software misread.
- ✗
Loose connection between the battery and motherboard
Why it's wrong here
A loose connection could cause random shutdowns, but it would not consistently occur at a specific remaining percentage. Additionally, the immediate power-on when connected to a charger suggests the battery itself is the problem, not the connection.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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