3.7V 140mAh Lithium Polymer Battery Pack 400840

SunKing 400840 3.7V 140mAh 0.518Wh lithium polymer battery pack delivers stable and efficient power in an ultra-thin, lightweight form factor. Engineered for low-power consumption and reliable performance, it is an ideal power solution for Bluetooth earphones, compact digital devices, and wearable electronics where space, weight, and energy efficiency are critical.

400840 Ultra-Thin Size – Only 4 mm thickness, perfectly suited for Bluetooth earphones and ultra-compact digital devices.
Stable 3.7 V Output – Provides consistent voltage for sensitive audio and wireless electronics.
140 mAh / 0.518 Wh Capacity – Optimized for lightweight designs with dependable cycle life.
Customizable – Size, capacity, connectors, and wire length tailored to your needs.

15+ Years Experience

Fully Customizable

E2E Support

Certified & Tested

Click to contact via email (sales@sunkingbattery.com)

Battery Specification
Model	SK 400840 3.7V 140mAh 0.518Wh	Type	Lithium Polymer Battery (LiPo)
Dimension	4840mm (T/W/L)	Weight	2g
S/P Configuration	1S	Chemistry	NMC
Nominal Voltage	3.7V	Charging Voltage	4.2V
Nominal Capacity / Energy	140mAh / 0.518Wh	Charge Termination Current	≤0.05C
Discharge Cut-off Voltage	2.45V	Standard Charge Current	70mA
Max Charge Current	100mA	Standard Discharge Current	70mA
Max Discharge Current	140mA	Internal Impedance	Less than 200 mΩ
Standard Cycles	400-500	Storage Temperature	20℃
Charge Temperature	0-45℃	Discharge Temperature	-10-65℃
BMS Protection Functions	Over-Charge Protection; Over-Discharge Protection; Over-Current Protection; Short Circuit Protection
Application	Wearables; Consumer Electronics; IoT Devices & Smart Home; Portable Medical Devices; Handheld Terminals; Mini UAV / RC Models; Smart Cards / ID Devices

15+ Years of Industry Experience

With over 15 years of experience in lithium battery design and manufacturing, we have supported customers across different industries — from early concept development to stable mass production.

This long-term industry focus allows us to understand common technical challenges and deliver solutions that are practical, scalable, and production-ready.

How We Work with Customers

We operate on a project-based cooperation model and work closely with customers throughout the entire development process:

Application analysis and requirement evaluation
Battery design and technical validation
Rapid prototyping and testing
Scalable manufacturing and delivery

Our in-house engineering team, supported by professional production and testing equipment, ensures efficient development cycles and consistent product quality.

Our Capabilities

Engineering & Manufacturing Capabilities

Our capabilities cover both development and production stages, enabling smooth transitions from prototype to mass production.

By integrating engineering support, controlled manufacturing processes, and structured testing, we help customers reduce development risk and shorten time to market.

Quality, Compliance & Legal Responsibility

All products are manufactured and supplied by Sunking Energy Technology Co., Ltd.,
ensuring product quality, regulatory compliance, and reliable international delivery.

Certifications such as UL, CE, RoHS, UN38.3, and MSDS are available upon customer request, depending on specific project requirements.

Trusted by Leading Brands

We have delivered customized lithium battery solutions for customers and brands such as:

Haier

SKYWORTH

CHANGHONG

Hello Bike

King Long Bus

Joyoung

Click to contact via email (sales@sunkingbattery.com)

Business Process FAQs

Are you the official SunKing Energy company?

Yes. We are Shenzhen SunKing Energy Technology Co., Ltd., founded in 2011 (Unified Social Credit Code: 9144030057002758X6).

sunkingbattery.com is our only official website. Headquartered in Huizhou, China, we operate multiple factories nationwide and serve long-term global customers. Official social media accounts are linked in the website header and footer.

What types of batteries do you offer?

We provide fully assembled lithium battery packs, including Li-Po battery packs, cylindrical battery packs (such as 18650), and multi-cell battery solutions.

All battery packs use only A-grade cells with guaranteed capacity. We never use recycled or substandard cells, ensuring stable performance and long-term reliability.

Not sure which battery fits your product? Share your application, voltage, capacity, or size, and our engineers will recommend the best solution.

Can you customize battery size, capacity, voltage, and connectors?

Yes. We offer full customization services, including battery dimensions, capacity, voltage configuration, BMS design, wire leads, connectors, and casing materials to meet your project requirements.

What information do I need to provide for a custom battery pack?

Please provide your application scenario, size limitations, required capacity and voltage, discharge rate, operating environment, and any mandatory certifications. This information helps us design the optimal lithium battery solution.

What are your MOQ requirements for custom lithium battery packs?

Since most lithium battery packs are custom-built, MOQ depends on your technical specifications and design complexity. Contact us to receive a clear MOQ based on your specific project.

What is your production lead time?

Sample lead time is typically around 5 working days. Mass production lead time ranges from 10 to 25 working days, excluding shipping.

Lead time may vary depending on material availability, but our stable supply chain ensures consistent and reliable delivery.

Do your lithium battery packs include safety protection?

Yes. All battery packs include basic BMS protection such as overcharge, over-discharge, overcurrent, and short-circuit protection.

Optional features including temperature sensors and advanced protection functions can be added based on application needs.

Which certifications can you provide for lithium batteries?

We support certifications including UN38.3, MSDS, CE, RoHS, and others depending on your target market and application requirements.

Certified battery packs can be supplied directly, or we can assist with custom certification processes for your project.

How do you guarantee lithium battery pack quality?

We implement strict IQC, IPQC, and OQC quality control processes and perform 100% capacity and safety testing before shipment to ensure consistent quality.

What is your warranty policy for battery packs?

Our standard warranty period is 12 months. Extended warranty terms are available for long-term cooperation partners and large-volume projects.

What shipping methods do you support for lithium batteries?

We support air freight, sea freight, rail transport, and express delivery, depending on destination, regulations, and lithium battery transport requirements.

Can you provide lithium battery samples for testing?

Yes, samples are available for testing and evaluation. Shipping costs are borne by the customer. Sample fees may apply for high-value or fully customized battery packs and are handled flexibly based on the project.

What after-sales support do you offer?

We provide technical guidance, troubleshooting support, and long-term after-sales service to ensure stable battery performance throughout the product lifecycle.