What Is an RTC Battery? Full Guide to Types & Uses

By Ufine, Updated on July 3, 2025

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In modern electronics, real-time tracking and time-sensitive operations are fundamental. At the heart of this capability lies a small but crucial component: the RTC battery. Whether you’re dealing with a laptop, embedded system, or industrial controller, an RTC (Real-Time Clock) battery ensures your system keeps track of time—even when the main power is off.

In this article, we explore everything about RTC batteries—from how they work, where they’re used, and how to replace them, to how to choose the right one. Let’s dive in.

Part 1. Learn RTC battery

An RTC battery powers a real-time clock (RTC) module, which keeps track of current time and date when the main system power is unavailable. RTCs are essential in systems that must maintain accurate time information through power outages, reboots, or long downtimes.

Without an RTC battery, your device would reset to a default time every time it loses power—a critical issue for applications like security systems, data logging devices, industrial controllers, and more.

Part 2. How an RTC battery works

An RTC module contains a tiny quartz crystal oscillator and low-power circuitry that runs continuously, drawing only microamps of current. The RTC battery provides just enough power to keep the clock ticking even when the main system is turned off.

Here’s how it works:

When the device is powered on, the RTC draws power from the main power supply.
Once the system shuts down or experiences a power cut, the RTC battery kicks in, ensuring uninterrupted timekeeping.
The battery is often connected directly to the RTC chip or integrated with the device’s motherboard.

This simple mechanism has critical implications—especially in devices where time stamping, scheduling, and logs must remain accurate regardless of power state.

Part 3. Applications of RTC batteries

RTC batteries are found in a wide range of devices across various industries:

Computers and Laptops

In personal computers, the RTC battery is often referred to as the CMOS battery, which maintains the BIOS settings and system time even when the computer is unplugged. Without it, your computer would reset to an incorrect time after every shutdown.

Embedded Systems and IoT Devices

In microcontroller-based systems like Arduino or Raspberry Pi, RTC modules (like DS1307 or DS3231) often rely on coin cell batteries to maintain time when the board loses power.

Medical Devices

Accurate timing is crucial in patient monitoring equipment, infusion pumps, and diagnostic machines. RTC batteries ensure data logging remains precise and reliable.

Industrial Automation

PLC systems, machine controllers, and industrial sensors rely on RTCs for logging operations, fault events, and scheduling tasks—even in harsh and unstable power environments.

Automotive Electronics

Vehicle ECUs use RTCs for time-sensitive operations like logging error codes, managing service intervals, and supporting GPS synchronization.

Part 4. Types of RTC batteries

Choosing the correct RTC battery depends on the device type, environment, and application lifespan. The main types include:

Coin Cell Batteries

These are the most common type, often used in consumer electronics and embedded systems.

Examples: CR2032, BR2032
Chemistry: Lithium manganese dioxide (Li-MnO₂)
Voltage: Usually 3V
Pros: Small, cost-effective, long shelf life
Cons: Not rechargeable

Rechargeable RTC Batteries

These are ideal for systems where the RTC gets frequent short-term use or where recharging is possible.

Examples: ML2032 (manganese lithium), LIR2032 (lithium-ion)
Voltage: Typically 3V to 3.6V
Pros: Rechargeable, eco-friendly
Cons: Lower cycle life compared to primary cells

Supercapacitors

Used as alternatives in some designs.

Pros: Extremely long cycle life
Cons: Higher self-discharge rates, sensitive to temperature

Each battery type serves a different niche and has to be selected carefully based on system requirements.

Part 5. Key specifications to consider

When selecting an RTC battery, consider the following parameters:

Voltage: Commonly 3V or 3.6V; must match the device’s requirement.
Capacity (mAh): Indicates how long the battery can power the RTC; higher values mean longer life.
Chemistry: Affects performance, rechargeability, and temperature tolerance.
Discharge Rate: Must be low to ensure battery longevity.
Size & Form Factor: Should fit securely in the available housing or battery holder.
Shelf Life: Coin cells often last 5–10 years depending on use and quality.

Understanding these specifications ensures reliable and long-term RTC performance.

Part 6. How long does an RTC battery last?

The longevity of an RTC battery depends on multiple factors, including usage, temperature, and the type of battery used.

Typical Lifespans

CR2032 (Non-rechargeable coin cell): 5–10 years
Rechargeable ML/LIR types: 2–5 years
Supercapacitors: Up to 10 years (but require periodic charging)

Factors That Affect Life:

Operating temperature: High temps accelerate degradation.
Load current: Devices with higher RTC power demands will drain the battery faster.
Usage environment: Humidity and dust can also impact life.

Signs of battery failure include incorrect date/time, BIOS resets, or loss of configuration settings.

Part 7. How to replace an RTC battery

Step-by-Step Guide for PCs and Laptops:

Power off and unplug the device.
Open the case and locate the motherboard.
Identify the RTC battery (usually a coin cell in a holder).
Carefully pry it out and replace it with a new one of the same model.
Power on the device and reconfigure the date/time if needed.

For Embedded Devices:

Many RTC modules have battery holders. Simply remove and insert the new battery.
For soldered batteries, desoldering is required, which should be done carefully to avoid damaging PCB traces.

Important Note: Always use ESD precautions and ensure the replacement battery meets the same voltage and chemistry specifications.

Part 8. RTC battery vs. CMOS battery: are they the same?

The terms RTC battery, CMOS battery, and BIOS battery are often used interchangeably, but here’s the distinction:

TermCommon UsePurposeRTC BatteryGeneral/Embedded systemsMaintains clock and timeCMOS BatteryDesktop/laptop computersMaintains BIOS/UEFI settingsBIOS BatteryOlder PCsSame as CMOS battery

In essence, all three serve the same goal—keeping the system time and settings intact when power is lost—but the term used depends on the device and context.

Part 9. Choosing the right RTC battery for your device

When selecting a suitable RTC battery, consider:

Device requirements: Check voltage, size, and compatibility.
Battery type: Choose between primary (non-rechargeable) or secondary (rechargeable).
Environmental conditions: Choose industrial-grade batteries for high or low-temperature environments.
Supplier reliability: Stick to trusted brands or custom battery manufacturers for critical systems.

Recommended RTC Battery Suppliers

Panasonic
Renata
Maxell
Ufine Battery (custom solutions for embedded, industrial, and low-temperature applications)

Ufine Battery, for example, specializes in custom lithium battery packs including RTC-compatible models. Their expertise in low-leakage, long-shelf-life, and compact cell design makes them a valuable partner for OEMs and device manufacturers. Contact Ufine Battery for tailored RTC battery solutions.

Part 10. Storage and maintenance tips

To maximize the shelf life and performance of RTC batteries:

Storage Guidelines

Store in a cool, dry environment (15–25°C optimal).
Avoid humidity and condensation.
Do not store near conductive materials.

Maintenance Tips

Periodically check battery voltage (especially in mission-critical devices).
Replace batteries before they fully discharge to prevent data loss.
Dispose of used batteries following environmental regulations.

Proper storage and proactive maintenance can prevent unexpected time resets and system malfunctions.

Part 11. RTC battery challenges in low-temperature or harsh environments

RTC batteries in extreme environments face unique challenges:

Common Issues

Decreased voltage output at sub-zero temperatures
Accelerated self-discharge
Cracking or leakage due to thermal cycling

Solutions

Use industrial-grade lithium cells rated for -40°C to +85°C.
Encapsulate the RTC and battery module for insulation.
Choose rechargeable lithium thionyl chloride batteries or coin cells with high-temperature tolerance.

Ufine Battery offers custom RTC battery solutions for devices that operate in freezing or high-heat conditions. Their experience with temperature-resistant chemistries ensures reliable timekeeping in demanding fields such as aerospace, mining, and outdoor surveillance.

Part 12. Conclusion

The humble RTC battery plays a vital role in maintaining time and configuration across a wide array of electronics. From laptops and embedded systems to industrial controllers, these small power sources ensure reliability and continuity.

Choosing the right RTC battery involves understanding voltage requirements, environmental conditions, battery chemistry, and lifespan. And for those with specialized needs, trusted manufacturers like Ufine Battery offer custom battery packs to meet the most demanding applications.

Whether you’re replacing a CMOS battery in a laptop or designing a time-sensitive embedded device, knowing your options and caring for your RTC battery ensures your systems run reliably—right on time.