Introduction
The CR85R is a type of coin‑cell battery characterized by a 1.5‑volt nominal voltage, an 8.5‑millimeter diameter, and a thickness of approximately 1.6 millimeters. Designed primarily for portable electronic devices that require a compact, lightweight power source, the CR85R has become a standard component in keyless entry remotes, small clocks, wireless sensors, and a variety of other low‑power applications. Unlike many primary lithium coin cells, the CR85R is rechargeable, allowing users to replace it with a new battery rather than dispose of it after a single use. This article surveys the development, technical specifications, applications, and environmental considerations associated with the CR85R battery.
History and Development
Origins of the Coin‑Cell Battery
The lineage of the CR85R can be traced back to the 1950s, when the first commercially viable lithium primary cells were introduced. Early designs, such as the CR2032 and CR2025, featured a 3‑volt chemistry and a diameter of 20 millimeters. As consumer electronics evolved toward smaller form factors, manufacturers began producing thinner, lower‑capacity cells to meet the demands of compact devices. By the early 1990s, the 8.5‑millimeter diameter cell - known simply as the CR85 - had emerged to power small key fobs and wireless remote controls.
Transition to Rechargeable Technology
The standard CR85 was a primary, non‑rechargeable cell, using a lithium‑metal anode and a manganese dioxide cathode. While reliable, the single‑use nature of the CR85 led to increased waste and higher operating costs for manufacturers of keyless entry systems. In response, several battery manufacturers in the late 1990s developed a rechargeable variant of the 8.5‑millimeter cell. This variant adopted a lithium‑polymer or lithium‑ion chemistry, enabling multiple charge–discharge cycles while maintaining the same form factor. The resulting battery was designated CR85R, where the “R” indicates rechargeability.
Standardization and Global Adoption
Following its introduction, the CR85R was incorporated into the International Electrotechnical Commission (IEC) and Underwriters Laboratories (UL) standards for small rechargeable cells. By the mid‑2000s, the CR85R had been adopted by a broad spectrum of manufacturers worldwide, becoming a staple in automotive and consumer electronics supply chains. Today, the CR85R is listed in the IEC 60086 series of coin cell specifications and is widely supported by battery management systems designed for low‑drain applications.
Physical Characteristics
Dimensions and Physical Design
The CR85R measures 8.5 millimeters in diameter and 1.6 millimeters in thickness. The cell is encased in a sealed plastic housing that protects the internal components from moisture and mechanical damage. A metal contact is provided on the top surface, allowing for easy insertion into devices. The bottom of the cell is sealed, ensuring that no internal electrolyte can escape during normal operation. The compact size enables integration into devices that are less than 20 millimeters in width.
Materials and Construction
The external housing is typically made of high‑density polyethylene or polypropylene, chosen for its chemical resistance and mechanical robustness. Internally, the cell contains a lithium‑ion or lithium‑polymer electrolyte, a graphite or lithium‑cobalt oxide cathode, and a lithium anode. The electrolyte is usually a polymer matrix that allows lithium ions to shuttle between the anode and cathode during charge and discharge cycles. The choice of electrolyte and electrode materials influences the cell’s capacity, voltage stability, and safety characteristics.
Chemical Composition and Electrochemistry
Electrochemical Reaction
During discharge, lithium ions move from the anode to the cathode through the electrolyte, generating a flow of electrons that powers the connected device. The general reaction for a lithium‑ion CR85R can be expressed as:
Li⁺ + e⁻ + CoO₂ → LiCoO₂
During charging, the reaction reverses, with lithium ions returning to the anode. The voltage produced is governed by the electrochemical potential difference between the anode and cathode materials, which in the case of CR85R cells is maintained at approximately 1.5 volts.
Capacity and Energy Density
The nominal capacity of the CR85R varies between 5 and 10 milliampere‑hours (mAh), depending on the manufacturer and specific chemistry. While this capacity is modest compared to larger batteries, it is sufficient for low‑drain applications that consume only a few milliamperes of current. The energy density - measured in watt‑hours per gram - is higher than that of conventional zinc‑carbon coin cells, allowing CR85R batteries to power devices for longer periods before replacement is necessary.
Internal Resistance and Temperature Dependence
Internal resistance in a CR85R typically ranges from 15 to 25 ohms. This resistance influences the battery’s ability to deliver current during short bursts of operation, such as when a remote control transmits a signal. Temperature also affects internal resistance: at low temperatures, resistance increases, reducing the battery’s effective output, whereas high temperatures can cause accelerated degradation. Therefore, devices that use CR85R batteries are often designed to operate within a temperature range of 0 °C to 40 °C to preserve performance.
Electrical Properties
Voltage Characteristics
The CR85R delivers a nominal voltage of 1.5 volts under no load. During discharge, the voltage remains stable for the majority of the capacity range, typically dropping below 1.4 volts only when the battery is nearly depleted. This flat voltage curve simplifies power management for devices, as it reduces the need for complex voltage regulation circuits.
Current Delivery and Discharge Curves
Because of its small size, the CR85R has a limited maximum continuous current output. In practice, the battery can safely supply currents up to 30 milliamperes, although most applications require only a few milliamperes. A typical discharge curve shows a gradual decline in voltage as capacity is consumed, followed by a sharper drop once the cell reaches the end of its usable life. Manufacturers provide discharge curves at various rates (e.g., 0.1C, 0.5C) to help designers predict battery behavior under different load conditions.
Charge Profile and Cycle Life
The CR85R is engineered for 400 to 600 charge–discharge cycles, though actual life depends on the depth of discharge and operating temperature. Chargers for these cells typically use a constant‑current followed by a constant‑voltage approach to prevent overcharging. Once the voltage stabilizes near 4.2 volts, the charger reduces current to avoid lithium plating on the anode. The total energy delivered over a battery’s life is usually around 4 to 6 watt‑hours, reflecting the balance between capacity and cycle durability.
Applications
Keyless Entry and Remote Controls
One of the primary uses of the CR85R is in keyless entry systems for automobiles and residential doors. These devices require a battery that can deliver intermittent bursts of power - typically 10 to 20 milliamperes - for signal transmission. The compact size and rechargeable nature of the CR85R reduce the overall cost of ownership for vehicle manufacturers and end users.
Wearable Electronics and Sensors
Due to its small footprint, the CR85R is also found in wearable devices such as fitness trackers, medical monitoring patches, and environmental sensors. In such applications, the battery’s low current consumption and flat voltage curve enable the integration of simple power management circuits, extending battery life and reducing device weight.
Industrial and Safety Equipment
In industrial settings, the CR85R powers handheld diagnostic tools, wireless field sensors, and safety equipment such as fire alarm tags. These devices often operate in harsh environments where reliability and longevity are paramount. The rechargeable design of the CR85R allows for easy maintenance and reduces the risk of battery depletion during critical operations.
Prototype Development and Hobbyist Projects
Engineers and hobbyists frequently employ CR85R batteries when prototyping small electronic projects. Their standard dimensions and readily available charging infrastructure make them an attractive choice for proof‑of‑concept devices, particularly those requiring a low‑drain power source.
Market and Manufacturers
Key Producers
Several manufacturers dominate the CR85R market. Companies such as Panasonic, Sony, Toshiba, and E-One supply a range of CR85R cells tailored to different specifications. In addition, Chinese manufacturers have entered the market, offering competitive pricing for both primary and rechargeable variants. While the core chemistry remains consistent across brands, subtle differences in capacity, internal resistance, and cycle life exist, influencing the choice of battery for specific applications.
Supply Chain and Distribution
CR85R batteries are distributed through a variety of channels, including specialty battery distributors, electronics component suppliers, and online marketplaces. Retailers often categorize these cells alongside other coin‑cell batteries, making them easily accessible for consumer electronics developers. In regions where keyless entry systems are prevalent, local automotive parts retailers maintain a stock of CR85R batteries to support after‑sales service.
Pricing Trends
The price of a CR85R battery varies based on volume, chemistry, and supplier. Bulk purchases for automotive manufacturers typically yield lower per‑unit costs, whereas small orders from hobbyists are priced higher. Over the past decade, advances in lithium‑polymer chemistry have kept manufacturing costs relatively stable, while the shift toward rechargeability has slightly increased the retail price compared to primary coin cells.
Environmental Impact and Recycling
Lifecycle Assessment
The environmental footprint of the CR85R is influenced by its rechargeable nature. While the production of lithium‑ion cells requires mining of lithium, cobalt, and nickel - processes that carry environmental and social costs - the longer lifespan of rechargeable batteries reduces the frequency of disposal and manufacturing waste. Comparative studies indicate that a rechargeable CR85R can offset the environmental impact of up to ten primary coin cells, assuming equivalent use patterns.
Recycling Programs
Many manufacturers have instituted take‑back and recycling programs for spent CR85R batteries. In the United States and Europe, the e‑waste directive mandates proper disposal of lithium‑ion batteries. Recycling involves recovering valuable metals such as lithium and cobalt, and safely disposing of electrolyte residues. Participation rates vary by region, but the overall trend is toward increased collection and recycling to minimize environmental harm.
Hazardous Materials
CR85R batteries contain small amounts of hazardous substances, including lithium salts and organic solvents. If a battery is punctured or short‑circuited, these materials can release toxic gases or cause thermal runaway. Proper handling procedures - such as avoiding puncture, using insulated charging contacts, and storing batteries in cool, dry environments - are essential to mitigate risks.
Safety and Handling
Thermal Management
The maximum operating temperature for a CR85R is typically 60 °C. Exposing the battery to higher temperatures can accelerate degradation and increase the risk of internal short circuits. Manufacturers recommend maintaining device operation within a temperature range of 0 °C to 40 °C for optimal performance and safety.
Charge Safety
When charging a CR85R battery, it is critical to use a charger designed for lithium‑ion chemistry. Chargers should implement a constant‑current, constant‑voltage (CCCV) charging protocol to prevent over‑charging, which can lead to overheating or cell swelling. Many chargers incorporate temperature sensors and cutoff circuits that stop charging if the temperature rises beyond a specified threshold.
Physical Damage and Short Circuits
Physical damage, such as puncture or crushing, can cause internal short circuits, leading to heat buildup or fire. Devices that incorporate CR85R cells should include protective circuitry, such as poly‑imide layers or metal shielding, to prevent accidental contact with the terminals. End users should be instructed to avoid inserting metal objects into battery compartments.
Regulatory Standards
Safety regulations for lithium‑ion batteries are codified in standards such as IEC 62133, UL 2054, and the UN 38.3 shipping requirement. Compliance with these standards ensures that CR85R batteries meet stringent criteria for safety testing, including thermal, mechanical, and electrical abuse tests.
Comparative Analysis with Similar Batteries
CR85 vs. CR85R
The primary distinction between the CR85 and CR85R lies in rechargeability. While the CR85 is a non‑rechargeable lithium‑metal cell with a nominal capacity of approximately 7 mAh and an operating voltage of 3 volts, the CR85R is a rechargeable lithium‑ion cell offering a similar form factor but delivering 1.5 volts. The voltage difference reflects the different chemistries; the CR85’s higher voltage makes it suitable for devices designed for a 3‑volt supply, whereas the CR85R’s lower voltage necessitates voltage regulation or a different power architecture.
Other Coin‑Cell Batteries
When comparing the CR85R to larger coin cells such as the CR2032 or CR2025, key differences emerge in capacity and size. The CR2032, with a 20‑millimeter diameter, delivers 200 to 240 mAh and 3 volts, suitable for higher‑current devices. The CR85R’s smaller size and lower voltage limit its application to low‑drain devices. However, the CR85R’s rechargeability offers a distinct advantage for devices that require frequent battery replacement.
Performance Metrics
Table of key performance metrics (not displayed due to formatting constraints) would typically include capacity, internal resistance, cycle life, operating temperature range, and nominal voltage for each battery type. Users selecting a battery must balance these metrics against device requirements, considering factors such as current draw, desired battery life, and space constraints.
Standards and Regulations
IEC 60086
The IEC 60086 series defines technical specifications for coin‑cell batteries, including dimensions, tolerances, and electrical parameters. CR85R cells conform to the IEC 60086‑2 standard for small rechargeable lithium‑ion cells. Adherence to these specifications ensures interchangeability across manufacturers and compatibility with standard battery holders.
UN 38.3
UN 38.3 is a shipping standard for lithium batteries, covering tests such as altitude simulation, over‑charge, short‑circuit, and mechanical impact. CR85R batteries that are shipped internationally must pass UN 38.3 to qualify for transport via air or sea.
EU E‑Waste Directive
EU Directive 2011/65/EU (the Waste Electrical and Electronic Equipment Directive) imposes obligations on manufacturers and importers to ensure the collection, recovery, and recycling of batteries. Compliance involves labeling, consumer notification, and reporting on recycling rates.
United States Hazardous Materials Regulations
The U.S. Department of Transportation’s Hazardous Materials Regulations (HMR) specify packaging, labeling, and documentation requirements for shipping lithium‑ion batteries. Products that include CR85R cells must adhere to these regulations when delivered to customers or when used in applications requiring battery removal for maintenance.
Future Outlook
Emerging Chemistries
Research into solid‑state lithium‑ion batteries offers potential for higher energy density and improved safety. If applied to the CR85R form factor, such advances could yield cells with higher capacity (up to 15 mAh) and lower internal resistance, extending battery life for low‑drain devices.
Integration with Wireless Power Transfer
Future developments may include wireless charging solutions for CR85R batteries. Technologies such as inductive coupling or resonant power transfer could eliminate the need for physical charging contacts, reducing wear on battery compartments and enabling “plug‑and‑charge” functionality in keyless entry systems.
Environmental Sustainability
Continued efforts to reduce the cobalt content and to develop cobalt‑free lithium‑ion chemistries will lessen the environmental burden of CR85R production. Coupled with increased recycling infrastructure, these developments may further position rechargeable coin‑cell batteries as a sustainable power solution.
Conclusion
The rechargeable CR85R battery represents a compact, durable power source for a diverse set of low‑current electronic devices. Its 1.5‑volt output, flat voltage curve, and rechargeable chemistry provide a balanced solution for applications ranging from automotive keyless entry to wearable sensors. While its small size imposes limits on current delivery, careful design of devices - accounting for thermal management, voltage regulation, and safety protection - enables the effective integration of CR85R batteries. As the market evolves, advances in lithium‑polymer technology and enhanced recycling initiatives promise to further solidify the role of rechargeable coin‑cell batteries in sustainable electronics.
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