LiPo Batteries for Electronic Shelf Labels: Selection Guide

How to Choose a Lithium Polymer Battery for Electronic Shelf Labels: Capacity, Size and Service Life

An electronic shelf label may spend almost the entire day asleep, then ask its battery to deliver a short burst of current for wireless communication, an e-paper update or an LED alert. This unusual load pattern makes ESL battery selection more complicated than simply matching a voltage and capacity.

A battery that performs well in a wearable device may not provide the same service life in a digital price tag. The ESL designer must consider sleep current, update frequency, pulse current, operating temperature, available space and the way the battery will be replaced or recharged.

Lithium polymer batteries can be a good choice for thin, rechargeable or feature-rich electronic shelf labels. However, they are not automatically the best solution for every ESL design. Many conventional labels still use primary lithium manganese dioxide batteries because of their low self-discharge and long storage life.

The right decision starts with the ESL’s actual operating profile.

What Type of Battery Is Used in an Electronic Shelf Label?

Most electronic shelf labels use an e-paper display combined with a low-power microcontroller and a wireless communication system such as Bluetooth Low Energy or a proprietary sub-GHz protocol.

Because e-paper retains an image without continuous power, the label can remain in sleep mode for long periods. Power is mainly required when the label receives data, refreshes its display, flashes an LED or communicates with a gateway.

Two battery categories are commonly considered.

Primary lithium batteries

Primary lithium manganese dioxide batteries, including coin cells and thin pouch-type cells, are widely used in low-power ESLs designed for several years of operation without charging.

Their main advantages include:

• Low self-discharge

• Long shelf life

• Simple power architecture

• No charging circuit

• Good suitability for infrequent display updates

The main limitation is that the battery must eventually be replaced or the label must be taken out of service.

Rechargeable lithium polymer batteries

Rechargeable lithium polymer batteries are more suitable when the ESL has a defined charging method or when its features demand more energy than a traditional low-power label.

Typical applications include:

• Rechargeable electronic price tags

• Large or frequently updated displays

• Labels with frequent LED activity

• Interactive tags with buttons or sensors

• Reusable logistics and warehouse labels

• Solar-assisted or contact-charged ESL systems

• Ultra-thin devices with a custom internal layout

A rechargeable LiPo cell generally has a nominal voltage of 3.7V or 3.85V, depending on its chemistry and charge-voltage specification. The charging IC, protection circuit and system voltage range must be designed around the selected cell.

It is also important not to identify a battery by its package alone. A thin, flexible pouch battery may be a rechargeable lithium-ion polymer cell or a non-rechargeable lithium manganese dioxide cell. These products have different voltages, charging requirements and service-life characteristics.

When Does a Lithium Polymer Battery Make Sense for an ESL?

A lithium polymer battery offers the greatest value when shape, thickness and rechargeability are more important than achieving the longest possible unattended service life from a primary cell.

Its pouch structure allows the battery to use rectangular or otherwise difficult internal spaces more effectively than a fixed-diameter coin cell. The cell can also be supplied with customized wires, connectors, tabs, protection circuits and temperature sensors.

LiPo should be considered when:

• The ESL includes charging contacts, a charging dock or energy harvesting

• The enclosure is too thin or irregular for standard coin cells

• The label refreshes more frequently than a conventional price tag

• The design includes LEDs, sensors, buttons or other interactive functions

• The battery is expected to be recharged during the product’s service life

• A standard battery cannot use the available internal space efficiently

For an ESL expected to operate for five, ten or more years without charging, primary lithium chemistry may still be the more practical option. A rechargeable LiPo cell should not be selected only because it fits the enclosure.

1. Start with the Available Space

Thickness is often the first mechanical constraint in an electronic shelf label. The battery sits behind or beside the display, while the enclosure must remain slim enough to fit standard shelf rails.

The design should account for more than the nominal dimensions shown on a cell drawing.

Allow room for thickness tolerance and expansion

A pouch cell should not be tightly compressed between the rear cover and the e-paper module. Cell thickness varies with manufacturing tolerance, state of charge, temperature and aging.

The required allowance should be agreed with the battery supplier using the actual cell specification. A fixed percentage should not be applied to every battery because expansion behavior depends on cell chemistry, capacity, construction and operating conditions.

The mechanical design should:

• Avoid direct pressure on the e-paper display

• Keep the cell away from sharp plastic ribs and screw bosses

• Provide clearance around the pouch edges and sealing area

• Prevent movement without rigidly compressing the cell

• Support wires and tabs against repeated pulling or vibration

• Consider battery removal and replacement during servicing

Foam, controlled adhesive areas or a suitable battery tray may be used to secure the battery. The chosen material must be compatible with the cell pouch and the expected temperature range.

Do not select the battery from screen size alone

A larger screen usually requires more energy per refresh, but screen size is not the only factor. Two labels with the same display size may have very different power requirements because of their radio protocol, update frequency, LED behavior and firmware.

The final battery dimensions should be based on the complete mechanical layout and measured power profile.

ESL design scenario	Typical battery design direction	Main points to verify
Compact, rechargeable label	Thin single-cell LiPo with custom lead or tabs	Minimum thickness, charging method and peak current
Medium label with frequent updates	Higher-capacity single-cell LiPo	Display refresh energy, radio events and usable capacity
Large or interactive label	Larger LiPo or parallel-cell solution	LED load, update frequency, protection circuit and charging time
Cold-storage label	Low-temperature cell or alternative primary chemistry	Pulse voltage, discharge performance and charging restrictions
Long-life label without charging	Primary lithium battery often preferred	Self-discharge, pulse capability and replacement strategy

This table is a design starting point, not a capacity recommendation. Capacity must be calculated from the device’s measured consumption.

2. Build a Realistic Power Budget

The average current of an ESL can look extremely low, but average current alone does not show whether the battery can support each display update.

A proper power budget should include:

• MCU sleep current

• Radio standby and receiving current

• Transmission current

• E-paper refresh current and duration

• LED current and flash time

• Sensor or button activity

• Voltage regulator losses

• Battery protection circuit consumption

• Charging-circuit quiescent current

• Expected update failures and retransmissions

Daily consumption can be estimated as:

Daily capacity use = sleep consumption + communication consumption + display refresh consumption + accessory consumption

For an individual event:

Event consumption in mAh = event current in mA × event duration in hours × events per day

The estimated load over the intended service period should then be adjusted for:

• Usable capacity at the system cutoff voltage

• Low-temperature capacity reduction

• Cell aging

• Self-discharge

• Conversion losses

• Production variation

• An engineering reserve

Do not calculate battery life from rated capacity divided by average current and stop there. That method ignores pulse-related voltage drop, temperature and the capacity that remains unavailable below the system’s minimum operating voltage.

Measure a working prototype

Component datasheets are useful during early design, but final battery selection should be based on measurements from a real ESL prototype.

Use a power analyzer or current-logging instrument to record:

• Deep-sleep current

• Gateway connection events

• A normal display update

• A full-screen or multi-color update

• LED operation

• Failed communication and retry events

• Operation at minimum and maximum temperatures

This measurement often reveals brief loads that are missing from the initial spreadsheet.

3. Check Pulse Current and End-of-Life Voltage

ESL radios and e-paper displays create short current pulses. Even when the total energy used by each pulse is small, the battery voltage can drop temporarily because of cell impedance.

The problem becomes more serious when:

• The battery is cold

• The remaining capacity is low

• The cell has aged

• The update current is high

• The protection circuit or connector adds resistance

If the voltage falls below the MCU’s undervoltage lockout threshold, the label may reset during an update. It may then restart, reconnect and repeat the same operation, consuming even more energy.

Battery evaluation should therefore include:

• DC internal resistance

• Voltage under the expected pulse load

• Pulse duration

• System cutoff voltage

• MCU brownout threshold

• Connector and wiring resistance

• Performance at low state of charge

• Performance at the lowest operating temperature

A larger rated capacity does not necessarily solve a pulse problem. Cell construction, electrode design, temperature and circuit resistance can be equally important.

4. Treat Service-Life Claims Carefully

An ESL battery-life claim is valid only when the operating conditions are defined.

A statement such as “up to ten years” should specify, or at least be based on:

• Number of updates per day

• Display type and number of colors

• Wireless communication frequency

• LED usage

• Operating temperature

• Network conditions

• Sleep current

• Battery chemistry

• System cutoff voltage

Rechargeable lithium polymer cells experience self-discharge and calendar aging even when they are not cycled frequently. Their long-term retention depends on temperature, state of charge and cell design. It is therefore unsafe to assume that every LiPo cell has an annual self-discharge rate of only one or two percent.

For a multi-year project, ask the supplier for retention, storage and aging data for the proposed cell. Accelerated test results should be reviewed together with actual application conditions.

If there is no charging method and the main requirement is the longest possible maintenance-free life, compare the LiPo design with a suitable primary lithium solution before finalizing the architecture.

5. Consider Cold-Chain Operation Early

Electronic shelf labels used in refrigerated displays and frozen-food areas present a different battery challenge.

At low temperatures, cell impedance rises and available capacity falls. The voltage drop during a radio transmission or e-paper refresh may become large enough to reset the system, even when the battery still contains usable energy.

Rechargeable lithium-ion batteries also have important charging restrictions at low temperatures. A standard LiPo cell should not be charged below the temperature specified by its manufacturer. The system may require:

• A low-temperature-qualified cell

• A charger with temperature sensing and charge inhibit

• Reduced charging current

• A different battery chemistry

• Firmware that limits high-load events when the battery is cold

• A larger voltage margin above the MCU cutoff

For freezer applications, test complete labels in a temperature chamber. Room-temperature capacity data cannot predict cold pulse performance accurately.

6. Evaluate Cell Construction Without Relying on One Label

Stacked electrode construction can be useful for thin cells and may offer good dimensional control. Wound construction is also widely used and can perform reliably when properly designed and manufactured.

It is too simple to assume that every stacked cell is better than every wound cell.

Instead, compare actual specifications and test data for:

• Thickness tolerance

• DC internal resistance

• Pulse performance

• Cycle life

• Storage behavior

• Swelling under specified conditions

• Low-temperature discharge

• High-temperature storage

• Lot-to-lot consistency

The right construction is the one that meets the ESL’s electrical and mechanical requirements with consistent production quality.

7. Confirm Safety and Transport Requirements

Compliance should be planned before the battery dimensions and electrical design are frozen.

Requirements vary by market and by whether the cell is shipped separately, installed in equipment or assembled into a protected battery pack. Common standards and tests may include:

• UN 38.3 for lithium battery transport testing

• IEC 62133-2 for portable sealed secondary lithium cells and batteries

• UL 1642 for lithium cells in relevant applications

• UL 2054 for certain household and commercial battery packs

• Regional requirements applying to the complete ESL product

A test report for one cell model does not automatically cover a modified construction, different cell combination or newly designed battery pack. Confirm that documents correspond to the exact battery supplied for the project.

The battery specification should also define:

• Maximum charge voltage

• Charge and discharge current

• Protection limits

• Operating and storage temperature

• Cell and pack identification

• Connector polarity

• Wire and tab requirements

• Production traceability

8. Questions to Ask an ESL Battery Supplier

Before ordering prototypes, provide the supplier with more than the desired voltage and capacity.

A useful ESL battery request should include:

1. Available battery compartment dimensions

2. Maximum permitted thickness

3. Nominal and operating voltage range

4. Measured sleep current

5. Maximum pulse current and duration

6. Number of updates per day

7. Radio protocol

8. Display size and color configuration

9. LED or sensor operating profile

10. Operating and storage temperature

11. Intended service life

12. Charging method, if applicable

13. Connector, wire, tab and polarity requirements

14. Required certifications and destination markets

15. Prototype and annual production quantities

Providing this information early makes it easier to determine whether a standard cell is suitable or whether a custom battery is justified.

Frequently Asked Questions

What is the best battery for an electronic shelf label?

There is no single best battery for every ESL. Primary lithium manganese dioxide batteries are widely used for long-life, low-update labels. Rechargeable lithium polymer batteries are better suited to thin, rechargeable, frequently updated or feature-rich ESL designs.

Can a lithium polymer battery power an ESL for ten years?

It should not be assumed without application-specific testing. Service life depends on cell chemistry, capacity, self-discharge, temperature, sleep current, update frequency and pulse performance. A rechargeable LiPo system also needs a realistic charging or maintenance strategy.

How is ESL battery capacity calculated?

Capacity should be calculated from measured sleep current, wireless events, display refreshes, LEDs and other loads. The result must then include losses, aging, temperature effects, usable capacity at the cutoff voltage and an engineering reserve.

Why does an ESL reset during a display update?

A common cause is a temporary voltage drop under pulse load. Cold temperature, an aged battery, high internal resistance, thin wires or connector resistance can push the supply voltage below the MCU’s minimum operating level.

Can a standard LiPo cell be used in a freezer ESL?

Only if the cell is rated and tested for the required temperature. Low-temperature discharge capability and charging restrictions must both be considered. Some cold-chain projects may be better served by a specialized low-temperature cell or primary lithium chemistry.

Final Thoughts

Selecting a lithium polymer battery for an electronic shelf label is a system-level engineering decision. Capacity matters, but so do thickness tolerance, pulse current, cutoff voltage, temperature, aging and charging strategy.

For a thin rechargeable ESL, a custom LiPo cell can make better use of the internal space and simplify mechanical integration. For a conventional label expected to operate for many years without charging, a primary lithium battery may provide a more suitable balance of service life and maintenance cost.

Cowon supports electronic shelf label battery projects with standard and customized battery options, including cell-size evaluation, wires, connectors, tabs, protection circuits and application-specific battery configuration.

To evaluate an ESL battery, send us the available battery space, voltage range, update frequency, operating temperature and expected annual quantity. Our team can help review the requirements and recommend a suitable battery solution.