Interview Questions for Battery Troubleshooting

Battery failure is a multifaceted issue stemming from a variety of causes, broadly categorized into internal and external factors. Internal failures often involve the battery’s inherent chemistry and construction. This includes degradation of the active materials within the cells, leading to reduced capacity and increased internal resistance. Think of it like a muscle slowly weakening with age and overuse. Another internal culprit is the growth of dendrites (tiny metallic structures) in some battery types, particularly lithium-ion, which can cause short circuits and potentially dangerous thermal runaway. External factors contribute significantly as well. Overcharging or deep discharging can severely damage the battery, much like overfilling or emptying a gas tank too frequently. Extreme temperatures, both hot and cold, accelerate degradation and reduce lifespan. Finally, physical damage, such as drops or impacts, can compromise the battery’s internal structure, leading to cell failure.

• Internal: Degradation of active materials, dendrite formation, manufacturing defects
• External: Overcharging/discharging, extreme temperatures, physical damage, misuse

The battery landscape is vast and diverse, with various chemistries catering to different applications. Let’s explore a few:

• Lead-Acid Batteries: These are the workhorses found in cars, trucks, and backup power systems. They’re relatively inexpensive and robust but have a lower energy density and shorter lifespan compared to other types.
• Lithium-ion Batteries (Li-ion): The dominant technology in portable electronics, electric vehicles, and grid-scale energy storage. They offer high energy density, long cycle life (depending on chemistry), and relatively quick charging times. However, they are more sensitive to temperature extremes and can pose safety risks if mishandled.
• Nickel-Cadmium (NiCd) Batteries: Once popular but now largely phased out due to environmental concerns (cadmium is toxic). They exhibited the “memory effect,” where repeated partial discharges reduced their capacity.
• Nickel-Metal Hydride (NiMH) Batteries: A less toxic alternative to NiCd, offering better energy density but still susceptible to the memory effect, though less pronounced.

The choice of battery depends heavily on the application’s specific energy requirements, operating conditions, cost constraints, and environmental considerations. For example, a high-performance electric vehicle would utilize high-energy density Li-ion cells, while a simple remote control might use an alkaline battery.

Diagnosing a faulty cell within a battery pack requires specialized equipment and a systematic approach. The process usually begins with measuring the open-circuit voltage (OCV) of each individual cell. A significant deviation from the expected voltage range for that specific battery chemistry is a strong indicator of a problem. Next, a battery analyzer, capable of measuring internal resistance, is used. Higher-than-normal internal resistance suggests a problem with the cell’s internal components. Further investigation might involve a capacity test, checking how much charge each cell can hold and deliver. Finally, visual inspection for signs of damage, bulging, or leakage is crucial. Thermal imaging can also be used to detect hot spots, indicating a cell that’s generating excessive heat due to internal short circuits.

For example, if you’re working with a 12-cell Li-ion battery pack, and one cell shows a significantly lower voltage (e.g., 2.5V instead of the expected 3.7V), or a much higher internal resistance than the others, it’s a prime suspect for failure.

Safety is paramount when working with batteries, especially those with higher voltages and energy densities. Always follow these precautions:

• Eye Protection: Wear safety glasses to protect against potential splashes of electrolyte or flying debris.
• Gloves: Use insulated gloves to prevent electric shock and skin irritation from electrolytes.
• Ventilation: Work in a well-ventilated area to avoid inhaling potentially harmful gases.
• Proper Tools: Use insulated tools to avoid short circuits.
• Fire Suppression: Have a suitable fire extinguisher (Class B or ABC) readily available, as some battery types can ignite.
• Disposal: Dispose of batteries according to local regulations, as they contain hazardous materials.
• Never disassemble a battery unless you’re properly trained and equipped to do so. Attempting to repair a damaged battery without the proper knowledge and safety measures can result in serious injury or even death.

A Battery Management System (BMS) is an electronic circuitry that acts as the central nervous system for a battery pack. It monitors and controls various parameters related to battery operation, ensuring its safe and efficient use. Think of it as a sophisticated guardian angel protecting your battery. A BMS is critical, particularly in applications involving multiple cells connected in series or parallel, where imbalances can lead to premature failure or safety hazards.

Key functions of a BMS include:

• Cell Voltage Monitoring: Continuously monitors the voltage of each individual cell.
• Current Monitoring: Measures the current flowing into and out of the battery pack.
• Temperature Monitoring: Tracks the temperature of individual cells and the overall pack.
• State of Charge (SOC) Estimation: Calculates the remaining capacity of the battery.
• State of Health (SOH) Estimation: Estimates the overall health and remaining lifespan of the battery.
• Charge/Discharge Control: Controls the charging and discharging process to optimize performance and safety.

The BMS safeguards the battery pack through various protective mechanisms that prevent damage and ensure safety. These include:

• Overcharge Protection: Prevents the battery from being overcharged, which can generate excessive heat and damage the cells.
• Overdischarge Protection: Prevents the battery from being discharged below a safe voltage level, which can permanently damage the cells.
• Overcurrent Protection: Cuts off the current flow if an excessive current is detected, preventing short circuits and overheating.
• Short Circuit Protection: Detects and interrupts short circuits to prevent damage and fire hazards.
• Overtemperature Protection: Disables charging or discharging if the battery temperature exceeds safe limits.
• Cell Balancing: Equalizes the state of charge among individual cells to maximize pack lifespan and efficiency.

These protections work in concert to prevent potential failures and ensure the battery remains within its safe operating parameters.

BMS failure modes can stem from various causes, leading to malfunctions and potential battery damage. Common failures include:

• Communication Errors: Failure in the communication between the BMS and other systems (e.g., vehicle control unit) can lead to incorrect readings or actions.
• Sensor Failures: Malfunctioning voltage, current, or temperature sensors can provide inaccurate data, leading to inappropriate protective actions or inaction.
• Component Failures: Internal components such as the microcontroller, power transistors, or relays can fail, disabling specific protection functions.
• Software Glitches: Bugs in the BMS firmware can cause incorrect calculations or unexpected behaviors.
• Overheating: Excessive heat can damage the BMS components, causing malfunctions.

These failures can have serious consequences, potentially leading to battery damage, safety hazards, and system malfunctions. Regular BMS diagnostics and firmware updates are crucial to prevent these issues.

Determining a battery’s State of Charge (SOC) involves measuring the remaining capacity relative to its total capacity. Think of it like checking the fuel gauge in your car – it tells you how much ‘fuel’ (energy) is left. There are several ways to do this:

• Voltage Measurement: A simple, yet less accurate method, especially for older batteries. The voltage drops as the battery discharges, but the relationship isn’t linear. For example, a 12V lead-acid battery might read 12.6V when fully charged and 11.8V when nearly depleted. However, this can vary widely depending on the battery’s chemistry and age.

• Coulomb Counting: This method involves measuring the current flowing into and out of the battery over time. By integrating this current over time, we can estimate the total charge transferred. It’s like meticulously tracking every drop of fuel used. This is a more accurate method but requires specialized equipment and is susceptible to errors if the current measurement is inaccurate.

• Battery Management System (BMS): Modern batteries often incorporate a BMS that monitors voltage, current, and temperature to provide a more accurate SOC estimate. The BMS uses sophisticated algorithms to account for various factors and provide a reliable reading. This is the most accurate and convenient method available.

The accuracy of SOC measurement depends on the method used and the condition of the battery. Calibration is crucial for maintaining accuracy over time. In practical applications, you’d choose the method that best suits the accuracy needed and the available resources. For example, a simple voltage check is fine for a quick assessment, but a BMS is essential for precise control in electric vehicles.

The State of Health (SOH) of a battery indicates its remaining capacity compared to its original capacity when new. Unlike SOC, which changes constantly with use, SOH reflects the battery’s long-term degradation. It’s like assessing the overall health of your car’s engine, not just its current fuel level. Testing SOH typically involves:

• Capacity Test: This involves fully charging the battery and then discharging it under controlled conditions while measuring the delivered capacity. Comparing this measured capacity to the rated capacity when new gives an estimate of the SOH. For example, if a battery rated at 100Ah now delivers only 80Ah, its SOH is 80%.

• Internal Resistance Measurement: As a battery ages, its internal resistance increases. Measuring this resistance provides an indication of the battery’s health. Higher internal resistance correlates with lower SOH. Specialized equipment, like a battery analyzer, is needed to perform this test accurately.

• Voltage and Impedance Spectroscopy: These more advanced techniques provide detailed information on the battery’s internal electrochemical processes, offering a more thorough assessment of SOH. This method is commonly used for research and development or high-precision battery applications.

It’s important to note that environmental conditions such as temperature can affect the results of SOH testing. Always ensure the battery is tested under controlled and standard conditions for accurate results. Interpreting the SOH data alongside voltage and other tests helps arrive at a more comprehensive diagnosis.

Different battery chemistries require different charging methods, and within each chemistry, varying charging techniques offer different trade-offs between speed, safety, and battery longevity. Here are some prominent methods:

• Constant Current (CC) Charging: The charger supplies a constant current until the battery reaches a specific voltage. It’s simple and fast but can lead to overcharging if not carefully controlled. Think of it like filling a tank with a constant flow of water until it’s full.

• Constant Voltage (CV) Charging: The charger maintains a constant voltage while the current gradually decreases as the battery charges. This prevents overcharging but is slower than CC charging. It’s like slowly topping off a tank as it nears capacity.

• Constant Current/Constant Voltage (CC/CV) Charging: This combines both CC and CV charging. It starts with CC charging for faster initial charging and then switches to CV charging to finish the charging process safely. This is the most common charging method for many rechargeable battery types. It’s a balance of speed and safety.

• Pulse Charging: This involves applying short pulses of current to the battery. It can be more efficient and gentler on the battery, but it’s more complex to implement.

• Adaptive Charging: Modern charging methods often use algorithms that adapt to the battery’s condition and temperature, optimizing the charging process for maximum efficiency and lifespan. This approach often leverages the capabilities of a sophisticated BMS.

The choice of charging method is crucial for optimal battery performance and life. Using an inappropriate method can lead to premature aging, reduced capacity, and even safety hazards. Always refer to the battery manufacturer’s recommendations for the best charging approach.

Proper battery charging techniques are essential for maximizing battery life, ensuring safety, and preventing premature failure. Improper charging can lead to various problems, including:

• Overcharging: This can generate excessive heat, causing damage to the battery’s internal components and potentially leading to fires or explosions. Imagine overfilling a water tank – it can overflow and cause damage.

• Undercharging: This can leave the battery in a state of deep discharge, reducing its capacity and lifespan. Think of consistently running a car on nearly empty fuel – it puts a lot of stress on the engine.

• Memory Effect (in some battery types): In certain battery chemistries like Nickel-Cadmium (NiCd), consistently charging before the battery is fully discharged can reduce its capacity. This is less of a concern for modern Lithium-ion batteries.

• Increased Internal Resistance: Improper charging can increase the internal resistance, leading to reduced performance and shortened lifespan.

Following the manufacturer’s charging recommendations is crucial. This typically includes the appropriate charging voltage, current, and temperature limits. Using a suitable charger designed for the specific battery chemistry is also paramount. Paying attention to warning signs like excessive heat or unusual smells during charging is essential to prevent damage or accidents.

Troubleshooting a battery charger involves systematically checking different components and parameters to identify the cause of malfunction. Here’s a step-by-step approach:

1. Visual Inspection: Start by examining the charger for any physical damage, such as loose wires, cracked casing, or burnt components. Look for signs of overheating, such as discoloration or melting of the plastic.

2. Input Voltage Check: Verify that the charger is receiving the correct input voltage from the power source. Use a multimeter to measure the voltage at the input terminals of the charger.

3. Output Voltage/Current Check: With the charger connected to a known good battery, check the output voltage and current using a multimeter. Compare these readings to the charger’s specifications. A significant deviation could indicate a problem in the charger’s circuitry.

4. Fuse Check: If the charger is not working, check the fuse. Replace it with a fuse of the same rating if it’s blown.

6. Internal Component Check: For more advanced troubleshooting, you might need to check individual components like diodes, transistors, and integrated circuits. This requires some electronics knowledge and appropriate testing equipment.

7. Load Test: Connect the charger to a simulated load (a resistor or a known good battery) to check if it can supply the rated current. This helps pinpoint issues in the power supply circuitry.

Remember safety precautions when troubleshooting electrical devices. Always disconnect the charger from the power source before performing any checks. If you’re not comfortable with electronics repair, it’s best to consult a qualified technician.

A failing battery exhibits various symptoms, depending on the type and the nature of the failure. Here are some common signs:

• Reduced Runtime: The battery depletes much faster than usual, indicating reduced capacity.

• Swelling or Bulging: This is a serious sign, especially in lithium-ion batteries, and can indicate internal damage or a risk of fire or explosion.

• Overheating: Excessive heat during charging or discharge is a warning sign of internal problems.

• Loss of Power: Sudden power loss or inconsistent performance points towards an issue with the battery’s ability to supply sufficient current.

• Low Voltage Under Load: The battery’s voltage drops significantly when a load is applied, indicating a high internal resistance and reduced capacity.

• Abnormal Voltage Readings: Unexpectedly high or low resting voltages can suggest internal cell imbalance or damage.

• Memory Effect (NiCd/NiMH): In older NiCd and NiMH batteries, a consistent decline in capacity may be observed even with proper charging.

If you observe any of these signs, it’s recommended to carefully assess the battery’s condition and consider replacement, especially if swelling or overheating is present. Ignoring these signs can lead to more serious problems and potential hazards.

Interpreting battery voltage readings requires understanding the battery’s chemistry and its typical voltage range. The voltage alone doesn’t provide a complete picture, but it gives a useful indication of the battery’s charge and health.

• Lead-Acid Batteries: A fully charged 12V lead-acid battery usually reads around 12.6-12.7V. A reading below 12V indicates a low state of charge, and a reading below 11.8V might suggest a serious problem. Remember that the voltage drops under load, so it’s important to measure the voltage both at rest and under load.

• Lithium-ion Batteries: The voltage range depends on the specific chemistry (e.g., LiFePO4, Li-ion polymer). A fully charged LiFePO4 battery typically reads around 3.6V per cell, while a discharged cell might be around 2.5V. Similarly, other lithium-ion chemistries have different nominal voltage ranges. It’s essential to consult the manufacturer’s specification for the expected voltage range.

• NiCd/NiMH Batteries: These batteries have a lower voltage per cell compared to lithium-ion, and their voltage doesn’t change as significantly with state of charge. The voltage remains relatively consistent until nearly fully discharged.

Voltage readings alone are not sufficient for diagnosing battery issues. They should be combined with other tests, such as capacity testing and internal resistance measurement, for a more comprehensive assessment. Always consult the battery’s datasheet or manufacturer’s specifications for reference ranges and interpreting voltage readings accurately.

Interpreting battery current readings involves understanding the flow of electricity into and out of the battery. A positive current indicates charging, while a negative current shows discharge. The magnitude of the current reflects the rate of charge or discharge; a higher current means faster charging or discharging. For example, a reading of +5A indicates a 5-ampere charging current, while -3A shows a 3-ampere discharge. Beyond the simple charge/discharge aspect, analyzing current readings over time reveals crucial information about the battery’s health. Consistent currents during charge and discharge indicate a healthy battery, while erratic fluctuations or significantly lower currents than expected can point to internal issues like degraded cells or increased internal resistance.

Consider this example: You’re testing a lithium-ion battery designed to charge at 2A. During charging, if you consistently see a current of 1A, it could indicate a problem with the charging circuit or a significant degradation of the battery’s ability to accept a charge.

Battery impedance, essentially the battery’s resistance to the flow of current, is a critical indicator of its health. A low impedance value generally suggests a healthy battery capable of delivering high currents efficiently. Conversely, a high impedance value points towards internal problems. We measure impedance using specialized equipment like impedance analyzers. The measurement is typically given in ohms (Ω) or milliohms (mΩ). An increase in impedance can be caused by factors such as cell degradation, sulfation (in lead-acid batteries), or internal shorting. It’s crucial to compare the measured impedance to the manufacturer’s specifications to determine whether the value is within acceptable limits.

For instance, a new lithium-ion battery might have an impedance of around 5 mΩ. If after several charge cycles, this rises to 50 mΩ, it’s a strong indication that the battery is degrading and its performance will be affected. The increase in impedance would lead to reduced power output and potentially increased heating.

Diagnosing internal short circuits in a battery requires careful examination and testing. A short circuit occurs when a low-resistance path develops between the positive and negative terminals within the battery, bypassing the normal discharge path. This can lead to excessive heat generation, rapid discharge, and even fire. Diagnosis involves a combination of techniques.

• Visual Inspection: Check for any visible signs of damage, such as bulging, swelling, or leaking.
• Voltage Measurement: A significantly lower than expected voltage under load can indicate an internal short.
• Current Measurement: High current draw even under low load, or current flow even when not in use, strongly suggests an internal short.
• Impedance Measurement: As mentioned earlier, significantly higher than expected impedance might signal an internal short.
• Advanced Techniques: Specialized techniques, like internal cell voltage measurement with a dedicated cell voltage meter, can isolate the faulty cell.

Example: A battery pack consistently shows a high current draw even when the connected device is off. This points to an internal short, possibly within a single cell, requiring further investigation and potentially replacement of the affected cell or the entire pack.

Cell imbalance in a battery pack occurs when the individual cells within the pack have different voltage levels. This is a common issue in series-connected battery packs, such as those found in electric vehicles or laptops. The imbalance can significantly reduce the overall pack’s capacity, performance, and lifespan. It can also lead to overheating and potential safety hazards.

Diagnosis typically involves:

• Individual Cell Voltage Measurement: Using a multimeter or a dedicated battery analyzer, measure the voltage of each cell individually. Significant deviations between cell voltages point to imbalance.
• Battery Management System (BMS) Data: Most modern battery packs have a BMS that monitors cell voltages. Reviewing BMS data can highlight imbalances before they become severe.

Example: In a 48V battery pack (12 cells in series, each nominally at 4V), if one cell has a voltage of 3.5V while others are at around 4V, this imbalance will affect the pack’s overall performance and needs to be addressed through balancing techniques.

Battery thermal runaway is a dangerous condition where an initial problem in a battery cell, such as internal short circuit or overcharging, triggers a cascading series of exothermic (heat-producing) reactions. This causes a rapid increase in temperature, further accelerating the reactions and potentially leading to fire or explosion. Think of it as a vicious cycle: the heat generated accelerates chemical reactions that generate more heat, creating a runaway effect.

Factors that contribute to thermal runaway include: excessive current, overcharging, cell damage, manufacturing defects, and external heat sources. The process often involves gas evolution, which can further increase pressure inside the battery, leading to potential venting or rupture.

Mitigating the risk of thermal runaway involves a multi-layered approach focusing on prevention and detection. Key strategies include:

• Proper Battery Design and Manufacturing: This involves using materials and designs that are less prone to thermal runaway. Including thermal fuses and pressure relief vents helps contain the consequences should runaway begin.
• Effective Battery Management Systems (BMS): A robust BMS monitors key parameters like cell voltage, temperature, and current. It intervenes to prevent overcharging, over-discharging, and excessive current draw. This early detection is critical.
• Thermal Management: Effective cooling systems, such as heat sinks or active cooling, can help dissipate heat generated by the battery, preventing thermal runaway.
• Safe Operating Procedures: Following manufacturers’ recommendations for charging, discharging, and storage prevents many potential causes of thermal runaway.
• Regular Inspection and Maintenance: Periodic inspections can help detect potential issues, such as physical damage or swelling, before they escalate.

Example: Using a BMS with over-temperature protection and active cooling in a high-power battery system significantly reduces the likelihood of thermal runaway by keeping cell temperatures within safe operating limits.

Battery overheating is a common problem with several potential causes, many of which can lead to thermal runaway if not addressed.

• Overcharging: Charging beyond the recommended voltage or current can generate excessive heat.
• Over-discharging: Discharging a battery below its minimum voltage level can also cause overheating, particularly in certain battery chemistries.
• High Current Discharge: Drawing high currents from the battery, especially for extended periods, generates significant heat due to internal resistance.
• Internal Short Circuits: As discussed earlier, internal short circuits cause significant energy dissipation as heat.
• External Heat Sources: Exposure to high ambient temperatures can exacerbate internal heat generation.
• Manufacturing Defects: Poorly manufactured batteries can have internal issues that cause overheating.
• Cell Imbalance: Unbalanced cells within a battery pack can lead to uneven heating and potential overheating of the most stressed cell.

Example: Rapid charging a smartphone with a damaged charging cable may generate significant heat, leading to overheating and potential battery damage.

Troubleshooting a battery that won’t charge involves a systematic approach. Think of it like a detective investigating a crime scene – we need to eliminate suspects one by one. First, we verify the power source. Is the charger plugged in correctly and functioning? A simple test with a voltmeter can confirm if the charger is outputting the correct voltage. Next, we examine the charging port on the device. Is it clean and free from debris that might be obstructing contact? A build-up of dust or corrosion can significantly impede charging. Then we check the battery terminals themselves for corrosion or damage. Clean them gently with a soft brush and a solution of baking soda and water, then rinse and dry thoroughly. If the problem persists, we’ll need to test the battery’s voltage directly using a multimeter. A significantly low voltage indicates a dead battery requiring replacement. Finally, the charging circuit within the device itself may be faulty; this usually requires professional repair.

• Step 1: Check the power source and charger.
• Step 2: Inspect the charging port for debris.
• Step 3: Examine and clean battery terminals.
• Step 4: Measure battery voltage with a multimeter.
• Step 5: Consider the possibility of a faulty charging circuit (professional help needed).

A battery discharging too quickly suggests an internal problem, parasitic drain, or a problem with the device itself. Imagine your battery as a water tank – if it’s emptying faster than normal, there’s a leak somewhere. First, we need to identify potential energy consumers. Are there apps running in the background? Are location services enabled? These are common culprits. Turning off unnecessary features can significantly improve battery life. We should also inspect the device for any physical damage. A cracked screen or a damaged charging port can lead to increased power consumption. Using a battery monitoring app can give insights into which apps are consuming the most power. Another diagnostic step is to perform a full discharge and recharge cycle to recalibrate the battery’s power readings. If the problem persists after these steps, it may be due to a failing battery or other internal component requiring professional diagnosis and possibly replacement.

• Step 1: Identify and close unnecessary apps and features.
• Step 2: Examine the device for physical damage.
• Step 3: Use a battery monitoring app to pinpoint power-hungry apps.
• Step 4: Conduct a full discharge/recharge cycle.
• Step 5: Consider a faulty battery or other hardware failure.

Battery troubleshooting requires a range of tools, much like a mechanic’s toolbox. Essential tools include a multimeter (for measuring voltage, current, and resistance), a battery analyzer (for more in-depth battery health assessments), a load tester (to simulate real-world usage), and specialized probes or connectors that are compatible with the type of battery under test (e.g., alligator clips or test leads). Additionally, we might need simple tools like a small brush, cotton swabs, and a cleaning solution (like baking soda and water) to clean battery terminals. Safety glasses and gloves are crucial for protection against potential hazards such as acid leaks.

My experience encompasses various battery testing equipment, ranging from basic multimeters to sophisticated battery analyzers. Multimeters are indispensable for measuring basic parameters like voltage and current, providing a quick check of the battery’s health. However, more advanced battery analyzers offer a deeper understanding of internal resistance, capacity, and overall health. These analyzers can identify issues like cell imbalance or degradation that a multimeter might miss. I’ve worked extensively with load testers, which help simulate actual usage scenarios and assess the battery’s performance under stress. These are particularly useful for identifying batteries that fail under load, even if they appear healthy under static testing. For specific battery chemistries, like lithium-ion, I’ve utilized specialized equipment for monitoring cell voltage and temperature during charging and discharging.

Documentation is critical for efficient troubleshooting. I maintain detailed records, typically using a combination of written notes and digital documentation. My written notes usually include the date, time, device details (model, serial number), initial symptoms, steps taken, measurements (voltage, current, resistance, etc.), and the final diagnosis. I often supplement these written notes with digital photos of the battery, charging port, and any visible damage. This approach provides clear traceability and facilitates future troubleshooting if similar problems occur. For larger organizations, specialized software or databases can be used to track and manage battery testing and maintenance efficiently.

Battery recycling is paramount for environmental responsibility. My experience includes following strict safety protocols when handling used batteries, specifically concerning the proper disposal of various battery chemistries. I’m familiar with local regulations and guidelines related to hazardous waste disposal. I know the procedures for safely dismantling and separating components to ensure that recyclable materials, like metals and plastics, are processed appropriately. Proper handling and disposal are essential to prevent environmental contamination and protect human health from hazardous chemicals often present in batteries. I am also aware of and follow the guidelines for responsible end-of-life management, including the use of certified recycling facilities.

One challenging case involved a seemingly simple problem: a laptop battery that wouldn’t hold a charge. Initial tests with a multimeter showed normal voltage, but the battery discharged rapidly under load. Standard troubleshooting steps, including cleaning terminals and checking the charger, yielded no results. Further investigation revealed subtle signs of internal swelling, almost invisible to the naked eye. This pointed toward a potential cell failure within the battery pack. After carefully examining the battery’s internal cells, I discovered one cell that showed significant internal resistance. This was not immediately apparent during basic testing. Replacing the faulty battery pack resolved the issue. The lesson learned was the importance of thorough visual inspection, even if initial testing suggests no obvious problems. Often, seemingly minor clues can lead to the correct diagnosis.