The nickel metal hydride battery is a safe, environmentally friendly, and versatile rechargeable solution, but how does it compare to lithium-ion and NiCd alternatives? This article explains its structure, electrochemical principles, performance metrics, and practical applications. You’ll discover key factors like voltage, capacity, cycle life, and self-discharge, helping you choose the right NiMH battery for devices from cameras to hybrid vehicles, maximizing efficiency, safety, and long-term value.
The global nickel-metal hydride (NiMH) battery market continues to demonstrate stable growth even in the evolving energy storage landscape. According to recent market research, the NiMH battery market size is estimated at approximately USD 3.6 billion in 2026, with forecasts projecting continued expansion to about USD 4.9 billion by 2033 at a compound annual growth rate (CAGR) of around 4.5% over the 2026–2033 period, driven by sustained demand in hybrid electric vehicles, industrial applications, and consumer electronics.
Main content:
- Key Takeaways
- What Is a NiMH Battery?
- Common Voltage / Capacity of NiMH batteries
- NiMH Battery Structure and Electrochemical Principles
- NiMH vs Li-Ion
- NiMH vs LiFePO₄
- NiMH vs Alkaline
- NiMH vs NiCd
- How to Determine If a Nickel Metal Hydride Battery Is Suitable For Your Device
- Key Performance Parameters of NiMH Batteries
- Charging Methods And Safety Mechanisms Of NiMH Batteries
- Advantages And Limitations Of NiMH Batteries
- Typical Application Scenarios Of NiMH Batteries
- Environmental, Recycling, And Economic Analysis
- How To Choose NiMH Batteries (Key Checklist)
- Future And Technology Trends Of NiMH Batteries
- Conclusion
- FAQs
Key Takeaways
- Nickel–Metal Hydride (NiMH) batteries are rechargeable cells that store energy by moving hydrogen atoms between a positive nickel oxyhydroxide electrode and a negative metal hydride alloy. Nominal voltage per cell is 1.2V, making them fully compatible with standard AA/AAA NiCd replacements.
- NiMH batteries offer specific energy of 60–120 Wh/kg and specific power of 250–1000 W/kg, providing stable high-current output. Typical cycle life ranges from 500–1000 cycles, while high-durability models exceed 2000 cycles, with low self-discharge (LSD) types retaining 70–85% charge after one year.
- Advantages: NiMH batteries are safer than lithium-ion, contain no toxic cadmium, and operate reliably between -25°C to 45°C. They maintain stable voltage under high load, making them ideal for digital cameras, power tools, wireless devices, and hybrid vehicle applications.
- Limitations: NiMH has lower energy density compared with Li-ion, higher weight, and standard self-discharge rates of 10–30% per month. High-temperature environments can shorten lifespan, so thermal management and proper charging strategies are critical.
- When choosing NiMH batteries, consider device voltage, power requirements, cycle frequency, and self-discharge type. For intermittent-use or standby devices, LSD/Eneloop types are recommended; for high-power, frequently used devices, standard high-rate NiMH batteries ensure stable performance.
What Is a NiMH Battery?
NiMH (Nickel–Metal Hydride) is a type of rechargeable battery that can be used many times instead of being thrown away like regular alkaline batteries.
- Positive electrode: Nickel hydroxide / Nickel oxyhydroxide (Ni(OH)₂ / NiOOH)
- Negative electrode: Special metal alloy that stores hydrogen (Metal Hydride)
- Nominal voltage: 1.2V per cell
In simple terms, a NiMH battery stores energy by moving hydrogen atoms between two metal parts inside the battery. When you charge it, electricity “pushes” the hydrogen into the negative part, and when you use it, the hydrogen moves back and produces power for your device. NiMH batteries are safer than many other types of batteries and are better for the environment than older nickel-cadmium (NiCd) batteries because they don’t contain toxic cadmium. They are often seen as a middle ground between old NiCd batteries and modern lithium-ion batteries
Common Voltage / Capacity of NiMH batteries
At the single-cell level, NiMH batteries have a stable nominal voltage of 1.2V, fully compatible with NiCd batteries, allowing seamless replacement in many devices. In practice, NiMH cells are often connected in series to form 2.4V, 3.6V, 4.8V, 7.2V, and other voltages to meet the requirements of walkie-talkies, RC models, power tools, and industrial control equipment.
In terms of capacity, NiMH batteries typically range from several hundred mAh to several thousand mAh. For example, common AA NiMH batteries usually have a capacity of 1800mAh–2700mAh, while AAA NiMH batteries mostly range from 600mAh–1100mAh. For battery packs consisting of multiple cells, capacity also depends on discharge rate, temperature conditions, and cell consistency.
NiMH Battery Structure and Electrochemical Principles
Basic structure
- Positive electrode: NiOOH
- Negative electrode: Metal Hydride (MH)
- Electrolyte: KOH
- Separator: Hydrophilic polyolefin / sulfonated separator
Structurally, NiMH batteries belong to typical sealed alkaline rechargeable batteries. The positive electrode material, centered on NiOOH, carries out redox reactions during charge and discharge. The negative electrode consists of metal hydride alloy, serving as the key unit for hydrogen storage and release. The electrolyte is usually an aqueous solution of potassium hydroxide (KOH), providing ionic conductivity without directly consuming itself.
The separator physically isolates the positive and negative electrodes while allowing OH⁻ ions to migrate freely. Its material choice directly affects internal resistance, rate performance, and cycle life. To ensure safety, modern NiMH rechargeable batteries commonly integrate safety valves and protective components, releasing pressure when it becomes excessive, reducing the risk of thermal runaway. This is one of the key reasons their safety profile is better than lithium-ion batteries.
Charge / discharge reaction mechanism
-
Negative electrode reaction:
H₂O + M + e⁻ ⇌ OH⁻ + MH -
Positive electrode reaction:
Ni(OH)₂ + OH⁻ ⇌ NiO(OH) + H₂O + e⁻
During charging, external electric energy drives hydrogen atoms to gradually embed into the negative electrode alloy lattice, forming a stable metal hydride structure. At the same time, Ni(OH)₂ in the positive electrode is oxidized to NiOOH. During discharge, this process reverses, releasing hydrogen stored in the alloy and delivering electrons through the external circuit.
Compared with lithium-ion batteries’ “lithium-ion intercalation / deintercalation” mechanism, NiMH battery reactions are closer to chemical adsorption and phase transition control, giving them higher stability under high temperature, overcharge, or mechanical shock, but also limiting maximum energy density.
Alloy system differences
-
AB5 type (mainstream): Rare earth + Ni/Co/Mn/Al
- AB2 type (high capacity): Ti/V + Zr/Ni
In manufacturing, NiMH battery performance differences often stem from the negative electrode alloy system. AB5 alloys are highly stable and mature, remaining the mainstream choice for consumer and industrial NiMH battery packs. AB2 alloys offer higher theoretical capacity but require tighter production control, higher costs, and reduced durability, so they are mostly used in high-performance applications.
Charge / discharge process
In practical use, NiMH battery charging relies on proper strategy, often using ΔV detection, temperature monitoring, or timer control to avoid overcharge. A reasonable charging algorithm not only increases usable capacity but also extends cycle life. During discharge, NiMH batteries exhibit a relatively flat voltage plateau, giving them an advantage over alkaline batteries in high-current devices.
NiMH vs Li-Ion
From a system perspective, the difference between NiMH and lithium-ion batteries is not just about energy density. NiMH cells have a nominal voltage of 1.2V, directly replacing standard AA cells and operating stably without a complex BMS. They are better suited for applications sensitive to safety, compatibility, and maintenance costs. In comparison, lithium-ion batteries have a nominal voltage of around 3.6V, higher energy density, but require a sophisticated BMS, increasing cost, design complexity, and safety requirements, making them more suitable for devices where size and weight are critical.
In practical use, many devices—such as cameras, power tools, and handheld instruments—can experience short-term high-current loads that challenge voltage stability. To assess how each chemistry responds under such conditions, TYCORUN conducted experiments showing that NiMH cells retain more consistent voltage than small-format lithium-ion cells during short-term overloads. This highlights the robustness of NiMH batteries in safety-sensitive or high-current applications.
NiMH vs LiFePO₄
Compared with LiFePO₄ batteries, NiMH does not excel in cycle life or energy efficiency. LiFePO₄ shows clear advantages in medium-to-large storage and power systems. However, NiMH offers simpler system structure, mature supply chain, and high standardization, maintaining good cost-performance in small devices, consumer products, and replacement markets. The two are more complementary in applications rather than direct substitutes.
NiMH vs Alkaline
Under high load conditions, NiMH rechargeable batteries can deliver stable voltage, while alkaline batteries experience rapid voltage drop. NiMH batteries show clear capacity advantages in high-current discharge scenarios, and their voltage plateau is more stable. Therefore, NiMH often provides longer actual usage time in digital cameras, wireless devices, and electric toys, remaining a mainstream choice among rechargeable alternatives.
NiMH vs NiCd
The core difference between NiMH and NiCd batteries is that NiMH does not contain cadmium, significantly improving environmental friendliness. Its energy density is 2–3 times that of NiCd. With environmental regulations tightening and technology maturing, NiMH has completely replaced NiCd in most consumer applications. Because of these advantages, NiMH batteries have systematically upgraded in regulations, market, and technology, becoming one of the most practical options among nickel-based rechargeable batteries.
How to Determine If a Nickel Metal Hydride Battery Is Suitable For Your Device
What voltage does your device require?
First, check your device’s voltage requirements. NiMH cells have a nominal voltage of 1.2V. If your device originally uses AA or AAA NiMH or NiCd batteries, NiMH is fully compatible. However, if your device requires 3.6V or higher per cell, a single NiMH cannot directly replace it and multiple cells must be connected in series.
Can your device handle high current output?
NiMH has a specific power of 250–1000 W/kg, performing stably under high current, making it suitable for digital cameras, handheld tools, wireless devices, and other high-power applications. If your device has low load and occasional use, ordinary high-self-discharge NiMH batteries may be less economical than low self-discharge (LSD / Eneloop) types.
Device usage frequency and storage needs
Ordinary NiMH batteries have a cycle life of about 500–1000 times, while high-durability types can exceed 2000 cycles. Low self-discharge batteries can retain 70–85% charge even after one year of storage. If your device is used intermittently or for long-term backup, low self-discharge models are more suitable. For frequent daily use or replacement devices, ordinary NiMH batteries are sufficient.
Can your device safely manage the battery?
NiMH batteries feature built-in safety valves, thermal fuses, and gas recombination mechanisms, controlling overcharge or over-discharge risks. However, if your device cannot limit over-discharge or uses multiple cells in series, special attention must be paid to charging strategy and polarity protection. By evaluating voltage, power, cycle life, self-discharge, and safety, users can quickly determine whether NiMH batteries are suitable for their devices and choose between ordinary or low self-discharge types.
Key Performance Parameters of NiMH Batteries
| Parameter | Typical Value / Range |
|---|---|
| Nominal Voltage | 1.2 V / cell |
| Specific Energy | 60–120 Wh/kg |
| Volumetric Energy Density | 140–300 Wh/L |
| Specific Power | 250–1000 W/kg |
| Cycle Life (Standard) | 500–1000 cycles |
| Cycle Life (High-Durability) | 2000+ cycles |
| Self-Discharge (Standard) | 10–30% / month |
| Self-Discharge (Low Self-Discharge / LSD) | 70–85% retained after 1 year |
| Operating Temperature | -25°C to +45°C |
| Electrolyte | Potassium Hydroxide (KOH) |
| Electrode Materials | NiOOH (positive) / Metal Hydride (negative) |
| Safety Features | Built-in pressure valve, thermal fuse, gas recombination |
Energy And Power Indicators
From the perspective of energy and power, NiMH battery sits in the middle range among rechargeable batteries. Its specific energy is 60–120 Wh/kg, and volumetric energy density is 140–300 Wh/L, which is significantly lower than lithium-ion battery but already at a high level among nickel-based batteries. At the same time, NiMH offers a specific power of 250–1000 W/kg, meaning it provides stable high-current output, especially suitable for digital cameras, wireless devices, power tools, medical equipment, and other scenarios sensitive to discharge stability. For these devices, continuous usable power is often more important than "theoretical runtime."
Cycle Life
Regarding cycle life, NiMH battery performance is highly model-dependent. Standard NiMH typically offers 500–1000 cycles, while high-durability products designed for industrial or professional applications can reach over 2000 cycles. To verify long-term performance, accelerated cycle tests at TYCORUN showed that NiMH cells maintained stable operation for over 1,800 cycles at moderate charge/discharge rates, confirming that high-durability NiMH can reliably meet the long-term usage requirements of consumer and industrial devices.
Although this metric is overall lower than that of LiFePO₄ batteries, it is sufficient for the full usage cycle of consumer-grade and small-to-medium power systems. For users who do not require extreme cycle counts but want stable performance over time, this “adequate and stable” cycle life is practically meaningful.
Self-Discharge Characteristics
Self-discharge is a key factor in determining whether NiMH is suitable for certain devices. Traditional NiMH battery can have a first-day self-discharge rate of 5–20% and a monthly self-discharge rate of about 10–30% when stored, making it less suitable for long-term standby or infrequently used devices. However, low self-discharge NiMH (LSD / Eneloop type) has significantly improved in this regard, retaining 70–85% of its charge even after one year of storage. In a series of spot checks conducted by the TYCORUN team on long-stored LSD batteries, we found that these cells remained powerful even after sitting in a drawer for a full year. This reinforces their reliability as a dependable energy source for emergency backup.
Charging Methods And Safety Mechanisms Of NiMH Batteries
Common Charging Strategies
NiMH battery charging methods are known for maturity and reliability. Common strategies include trickle charging (C/30 ~ C/10) for long-term and safe energy replenishment; ΔV (negative delta voltage) detection to determine full charge status; ΔT (temperature rise rate) monitoring to improve charging accuracy; and a combination of constant-current fast charging plus trickle top-up. These strategies allow NiMH rechargeable battery to charge safely without relying on complex BMS, making it especially suitable for devices sensitive to system cost and control complexity.
Safety Design
In terms of safety mechanisms, NiMH battery inherently features multiple passive protective structures, including built-in safety valves (for pressure release under abnormal conditions), resettable thermal fuses, and gas recombination catalytic mechanisms (H₂ + O₂ → H₂O). This design enables NiMH to maintain high safety margins under mild overcharge or environmental fluctuations, which is a key reason it is widely used in medical devices, children’s products, and industrial backup systems.
Overcharge And Overdischarge Risks
Although NiMH battery has high safety, risks still exist under improper usage conditions. During overcharge, hydrogen generation may occur inside the battery, causing temperature rise and triggering the pressure relief mechanism. In multi-cell battery systems, overdischarge can more easily cause reverse polarity damage, resulting in irreversible effects on the cells. Therefore, in practical applications, proper charge management and avoidance of deep discharge remain critical for extending NiMH battery lifespan.
Advantages And Limitations Of NiMH Batteries
| Feature | Advantage | Limitation |
|---|---|---|
| Environmental | Cadmium-free, recyclable | Requires proper recycling |
| High-Rate Discharge | Stable output | Generates heat under heavy load |
| Temperature Range | -25°C to 45°C | Performance drops at extremes |
| Safety | Low thermal runaway risk | Overcharge/discharge still harmful |
| Cost | Lower than Li-ion | More cells needed for same energy |
| Energy Density | Moderate, reliable | Lower than Li-ion |
| Self-Discharge | LSD retains 70–85% per year | None |
| Voltage Stability | Stable under high load | Drops under extreme cold/deep discharge |
| Compatibility | AA/AAA NiCd replacements | Needs multiple cells for high voltage |
| Weight | Durable, safe | Heavier than Li-ion/LiFePO₄ |
Core Advantages
One of the major advantages of NiMH battery is environmental friendliness. It contains no cadmium (Cd) and is fully recyclable, making it more compliant with modern environmental regulations than NiCd battery. Specifically, NiMH technology aligns with the Regulation (EU) 2023/1542, which imposes strict requirements on carbon footprint declarations and sets ambitious material recovery targets, including a 95% recovery rate for nickel by 2031.
At the same time, it has strong high-rate discharge capability, providing stable high-current output in high-power devices without voltage sag. NiMH operates reliably over a wide temperature range, generally -25°C to 45°C, suitable for various indoor and outdoor environments. Safety is another highlight; its risk of thermal runaway is low, and even under accidental overcharge or temperature fluctuations, it is unlikely to explode or catch fire. Additionally, in certain applications, NiMH rechargeable battery costs less than lithium-ion battery, maintaining competitiveness in consumer batteries and some industrial devices.
Main Limitations
However, NiMH battery also has some limitations. Its energy density is lower than lithium-ion battery, making it less efficient in devices with strict volume and weight constraints. Standard NiMH has a relatively high self-discharge rate, causing significant charge loss during long-term storage, though LSD / Eneloop products have improved this aspect.
In high-temperature environments, NiMH lifespan decreases significantly, requiring additional attention to heat dissipation and environmental control. Furthermore, NiMH is heavier compared to lithium-ion or LiFePO₄ batteries of the same capacity, which may add burden in portable devices. Overall, NiMH's strengths lie in safety, cost, and high-power output, but trade-offs exist in energy density and weight/volume.
Typical Application Scenarios Of NiMH Batteries
Consumer Electronics
NiMH rechargeable battery is widely used in consumer electronics, especially AA / AAA standard sizes. It is suitable for digital cameras, flashlights, toys, and remote controls, providing more stable discharge performance and the convenience of rechargeable repeated use compared with alkaline batteries.
Industrial And Medical
In industrial and medical fields, NiMH battery is often used as backup power to ensure devices continue working during power outages or emergencies. Typical applications include emergency power for medical devices, various instruments, and emergency lighting systems. NiMH’s safety and high-rate discharge capabilities make it highly reliable in critical equipment.
Hybrid Vehicles
In automotive power applications, NiMH battery was the core energy storage unit of first-generation HEV (Hybrid Electric Vehicle) mainstream solutions. Representative models include the early Toyota Prius, where the power system relied on NiMH battery for high-power output while meeting durability and safety requirements. Although some modern models have switched to lithium-ion battery, NiMH still holds an important position in HEV history and certain applications.
Renewable Energy And Energy Storage
In renewable energy and energy storage systems, NiMH rechargeable battery can be used for off-grid solar systems, small wind power storage, and remote area power supply. It can withstand frequent charge and discharge cycles, provide stable voltage output, and benefits from mature technology and a well-established supply chain, making it a reliable choice for small-scale storage, backup power, and microgrid solutions.
Environmental, Recycling, And Economic Analysis
Environmental Impact
NiMH battery has clear advantages in environmental protection. It contains no heavy metal cadmium (Cd), making it more eco-friendly compared with NiCd or some traditional batteries. At the same time, NiMH has high nickel content, providing clear recycling value and enabling effective material reuse in recycling systems. Therefore, NiMH rechargeable battery is more likely to comply with modern environmental regulations in both consumer and industrial applications.
Recycling System
NiMH battery recycling technology is already quite mature, with recovery rates higher than many lithium systems (Lithium-ion / LiFePO₄). Through professional recycling and smelting processes, nickel, rare earth metals, and other materials can be recovered, reducing environmental pollution and realizing the economic value of materials. This gives NiMH battery a long-term sustainability advantage.
Market Status
Although NiMH battery is no longer the mainstream power battery and is gradually replaced by lithium-ion in electric vehicles or large-scale energy storage, it still persists in cost-sensitive and high-safety scenarios. Examples include low-power hybrid vehicles, consumer replacement markets, and industrial backup power, where NiMH rechargeable battery continues to be widely used.
How To Choose NiMH Batteries (Key Checklist)
Clarify Purpose And Device Requirements
- Determine whether the battery will be used in high-power devices (such as digital cameras, handheld power tools) or low-power devices (remote controls, toys).
- Confirm whether the device functions as a backup power source or a frequently used primary power supply to decide between standard or low self-discharge (LSD / Eneloop type) batteries.
- Consider the operating temperature of the environment. If the device frequently works under high or low temperatures, choose NiMH battery with good temperature tolerance.
Match Voltage And Battery Size
- Check the required cell voltage and total battery voltage to ensure that NiMH can directly replace the existing battery or meet voltage requirements through series combination.
- Pay attention to battery size (AA, AAA, C, D, etc.) to ensure compatibility with the device battery compartment, avoiding installation issues caused by oversized or undersized batteries.
- Confirm connector type or polarity design matches device requirements, especially for industrial or specialized equipment using unique interfaces.
Select Standard Or Low Self-Discharge (LSD) Type
- For devices with intermittent use or long-term standby, prioritize LSD / Eneloop type batteries to reduce energy loss caused by self-discharge.
- For high-frequency use or regularly replaced devices, standard NiMH battery is acceptable, offering convenient charging and lower cost.
- Combine usage cycle and charging habits to select the most suitable type, extending battery lifespan and usage efficiency.
Confirm Discharge Capability And Power Output
- Check the device's maximum discharge current to ensure NiMH specific power can reliably meet requirements, avoiding voltage drop or device startup failure.
- For high-load devices (camera flash, handheld power tools), choosing high-rate NiMH battery ensures stable performance.
- For low-power devices, standard discharge capability is sufficient, but short-term high-current demands must still be met.
Pay Attention To Cycle Life And Warranty
- Understand the cycle life of the chosen NiMH battery: standard types typically offer 500–1000 cycles, while high-durability models can exceed 2000 cycles.
- Check manufacturer warranty policies and after-sales service to ensure replacement or repair is possible during long-term use.
- If the device is used frequently or requires repeated battery replacement, cycle life and warranty significantly impact total cost and user experience.
Ensure Charger Compatibility And Safety
- Confirm that the selected NiMH battery is fully compatible with the existing charger to avoid overvoltage or incomplete charging.
- Choose chargers with smart charging functions or safety protection to reduce risks of overcharge, overdischarge, and temperature rise.
- For multi-cell or high-capacity devices, ensure the charger supports balanced charging and multi-cell management, preventing polarity reversal or thermal runaway.
Consider Overall Cost And Sustainability
- Compare battery unit price, cycle life, and operating cost to choose the most economical and practical solution.
- If environmental protection and recyclability are important, prioritize NiMH battery, as recycling technology is mature and nickel content is high, providing both economic and ecological value.
- Combine device usage cycle and maintenance cost to make a long-term investment assessment, rather than judging solely by unit price.
Future And Technology Trends Of NiMH Batteries
Technology Improvement Directions
Future NiMH battery improvements will focus on three main directions. First, increasing energy density to make NiMH more competitive in space-constrained applications. Second, reducing self-discharge rate so the battery retains high charge even after long-term storage, improving efficiency in standby and consumer applications. Third, optimizing charge/discharge efficiency and cycle life through new separator and alloy systems, enhancing durability and safety, supporting high-power and long-life applications.
Long-Term Positioning
In the long term, NiMH battery will not directly compete with lithium-ion battery but will be positioned as a safe, durable, and cost-effective energy storage solution. In consumer replacement batteries, industrial backup power, low-power HEVs, and remote area energy storage systems, NiMH will maintain a stable market share. With mature supply chains, low cost, and safety advantages, NiMH rechargeable battery will continue to have significant value and potential in future applications.
Conclusion
Nickel metal hydride batteries provide a reliable, safe, and cost-effective energy solution for a wide range of devices. By understanding voltage, capacity, and self-discharge, you can select the best battery for your needs.
FAQs
Are NiMH batteries better than lithium?
NiMH batteries are not generally better than lithium-ion in energy density or weight. They excel in safety, cost-effectiveness, and environmental friendliness, making them suitable for devices where reliability, compatibility, and simpler charging systems matter more than compact size or maximum energy storage.
What is the problem with nickel metal hydride batteries?
The main issues with nickel metal hydride batteries are lower energy density, higher weight, and moderate self-discharge. They lose charge faster during storage and can be bulkier than lithium-ion, requiring careful selection based on device load, usage frequency, and thermal conditions.
How many years will a NiMH battery last?
A typical NiMH battery lasts 3–5 years with normal use. High-durability models can exceed 7 years. Lifespan depends on cycle count, charging methods, storage conditions, and temperature, making proper maintenance and avoiding deep discharge essential for longevity.
Why does Toyota still use NiMH?
Toyota continues using NiMH in certain hybrid vehicles due to proven safety, long-term reliability, and cost-effectiveness. NiMH batteries tolerate high-rate discharge, temperature fluctuations, and simpler battery management, offering consistent performance for HEVs in diverse driving conditions.
Can nickel metal hydride batteries catch fire?
NiMH batteries have a very low risk of catching fire under normal use. Built-in safety valves, thermal fuses, and gas recombination mechanisms prevent thermal runaway, making them safer than lithium-ion in consumer devices, emergency systems, and industrial applications.
How to tell if a battery is about to explode?
Signs include excessive swelling, leakage, overheating, or unusual pressure release. NiMH batteries rarely explode, but abnormal charge/discharge, short circuits, or physical damage can trigger safety mechanisms, warning users to stop use and safely replace the battery.
