Samsung 40T 21700
4000mAh / 35A
High-performance 4.0Ah 21700 lithium-ion cell designed for demanding applications that need a strong mix of energy, discharge current, and voltage stability.
Samsung 40T 21700 4000mAh 35A Battery (40T5)
The Samsung 40T is a high-drain 21700 power cell that balances 4000mAh-class capacity with a strong current rating. Compared with many higher-capacity 21700 cells, the 40T is positioned more toward power delivery and lower voltage sag under high load while still preserving useful runtime for demanding devices.
Samsung’s abridged specification also lists 45A with an 80°C surface-temperature cut, so the 45A value should be presented as a temperature-controlled condition rather than an unrestricted continuous rating.
| Brand / Model | Samsung SDI INR21700-40T, 40T5 listing variant |
|---|---|
| Cell Type | 21700 cylindrical lithium-ion rechargeable cell, flat top, unprotected |
| Standard Discharge Capacity | Minimum 4000mAh at 0.2C / 800mA discharge to 2.5V |
| Rated Discharge Capacity | Minimum 3900mAh at 10A discharge to 2.5V |
| Nominal Voltage | 3.6V |
| Charge Cut-Off Voltage | 4.20V |
| Discharge Cut-Off Voltage | 2.50V end-of-discharge |
| Standard Charge | CC-CV, 2A, 4.20V, 200mA cut-off |
| Rated Charge | CC-CV, 6A, 4.20V, 100mA cut-off |
| Charging Time | Standard charge approx. 180 minutes; rated charge approx. 70 minutes |
| Continuous Discharge | 35A without temperature cut recommended headline rating |
| Temperature-Cut Condition | 45A with 80°C surface-temperature cut requires thermal control |
| Cycle-Life Criterion | ≥2400mAh after 250 cycles, 6A charge and 35A discharge to 2.5V at 25°C |
| Storage Recovery | ≥3510mAh after 30 days at 60°C under the listed recovery test |
| Ambient Temperature | Charge: 0°C to 45°C / Discharge: -20°C to 60°C |
| Surface Temperature | Charge: 0°C to 50°C / Discharge: -20°C to 80°C; recommended re-discharge release <60°C |
| Dimensions | 21.22mm max diameter × 70.30mm max height, with tube |
| Weight | 70.0g max; live listing shows approx. 67g |
| Protection | No integrated protection circuit. Use compatible device-level or pack-level protection. |
Electrical operating envelope at a glance.
These quick-reference visuals summarize the cell’s current ratings, voltage window, energy estimate, and C-rate interpretation.
1. Current Capability Stack
Charge and discharge thresholds shown together for quick product-page comparison.
2. Voltage Operating Window
Per-cell voltage limits for charger, BMS, and pack configuration.
3. Capacity and Energy Translation
Nominal watt-hours are calculated from standard capacity and nominal voltage.
4. C-Rate Conversion
For a 4000mAh cell, 1C equals approximately 4A.
| 2A | 0.5C standard charge |
|---|---|
| 6A | 1.5C rated charge |
| 10A | 2.5C rated capacity test |
| 35A | 8.75C continuous discharge without temperature cut |
| 45A | 11.25C discharge with 80°C temperature cut |
High-drain performance should be evaluated by voltage sag and temperature rise.
The Samsung 40T is intended to maintain useful capacity while supporting high current. The rated capacity test uses 10A discharge, while the cycle-life test uses 35A discharge at 25°C. The 45A condition is specifically tied to an 80°C temperature cut, making thermal monitoring central to any design that pushes the cell above the 35A continuous headline rating.
The simplified discharge graph below visualizes voltage versus capacity under moderate, high, and temperature-controlled discharge conditions. It is intentionally product-page friendly and should be treated as an explanatory graphic, not a digitized laboratory curve.
Rating-language summary
| 35A | Use as the primary continuous-discharge rating. |
|---|---|
| 45A | Temperature-controlled condition with 80°C surface-temperature cut. |
| 10A | Rated discharge capacity test condition. |
| 6A | Rated charge current with 100mA cut-off. |
| Design takeaway | Pack-level output should be derated for heat, interconnect resistance, BMS limits, and duty cycle. |
5. Simplified Discharge-Curve Graph
Voltage vs. capacity illustration for 10A, 35A, and 45A temperature-cut operation. Simplified for product-page visualization.
6. Idealized Runtime by Constant Current
Ideal runtime using 4000mAh standard capacity before voltage sag, BMS cut-off, heat, and efficiency losses.
Temperature, charge current, and storage conditions.
Samsung separates ambient and cell-surface temperature limits. High-current designs should place thermal sensing near the hottest cell-surface location in the pack.
7. Charge Profile Reference
Standard charge is 2A CC-CV; rated charge is 6A CC-CV to 4.20V.
8. Thermal Operating Envelope
Ambient and cell-surface temperature ranges from the abridged specification.
9. Cycle-Life Visualization
Published criterion: ≥2400mAh after 250 cycles under 6A charge and 35A discharge conditions.
10. Storage Recovery
Storage retention criterion from the abridged specification.
21700 dimensional envelope for holders, weld fixtures, and pack CAD.
Use the specification maximum dimensions for holder fit, pack spacing, insulator design, and weld fixture clearance.
11. Cell Dimension Diagram
Mechanical envelope based on the Samsung outline drawing.
12. Pack Scaling Formulas
Quick math for series/parallel planning. Validate current limits thermally and electrically.
Pack Voltage ≈ Series Count × 3.6V
Pack Capacity ≈ Parallel Count × 4.0Ah
Pack Energy ≈ S × P × 14.4Wh
Conservative Pack Current ≈ P × 35A
13. Example Parallel Scaling
Approximate scaling using 35A continuous cell-level reference, not a finished pack guarantee.
| 1P | 4.0Ah, 14.4Wh, 35A continuous cell-level reference |
|---|---|
| 2P | 8.0Ah, 28.8Wh, 70A continuous cell-level reference |
| 3P | 12.0Ah, 43.2Wh, 105A continuous cell-level reference |
| 4P | 16.0Ah, 57.6Wh, 140A continuous cell-level reference |
| 5P | 20.0Ah, 72.0Wh, 175A continuous cell-level reference |
14. Common Series Voltage Examples
Nominal voltage examples only. Full-charge and cut-off pack voltages scale separately.
| 1S | 3.6V nominal / 4.2V full / 2.5V cut-off |
|---|---|
| 3S | 10.8V nominal / 12.6V full / 7.5V cut-off |
| 4S | 14.4V nominal / 16.8V full / 10.0V cut-off |
| 5S | 18.0V nominal / 21.0V full / 12.5V cut-off |
| 10S | 36.0V nominal / 42.0V full / 25.0V cut-off |
| 13S | 46.8V nominal / 54.6V full / 32.5V cut-off |
Use the 40T inside a temperature-monitored, current-limited system.
The 40T is a high-drain unprotected bare cell. Professional implementation requires a charger/BMS strategy that respects voltage, current, temperature, and interconnect limits.
15. Suggested Control Threshold Map
System-level control guidance derived from the abridged specification.
| Charge upper limit | 4.20V per cell |
|---|---|
| Discharge floor | 2.50V per cell |
| Charge ambient range | 0°C to 45°C |
| Discharge ambient range | -20°C to 60°C |
| Surface discharge OTP | Protection should not exceed 80°C at the hottest cell surface |
| Current control | Use 35A continuous unless the system is designed around the 45A temperature-cut condition |
16. Risk-Control Checklist
Recommended pack-building and use practices.
- Use only in devices or packs designed for lithium-ion 21700 cylindrical cells.
- Use a BMS or controller that monitors voltage, current, and temperature.
- Do not charge above 4.20V or discharge below 2.50V per cell.
- Derate current for ambient temperature, enclosure airflow, and cell aging.
- Never carry loose cells with conductive objects such as keys, coins, tools, or metal cases.
- Spot weld for pack assembly; do not solder directly to the cell body.
- Inspect wraps and top insulator rings before use.
- Validate pack busbar, nickel, wiring, fuse, and BMS sizing under real load.
Best suited for high-drain systems that need both power and 4Ah-class runtime.
Power Tools
- Strong fit for high-current cordless tool packs.
- Good balance of current and runtime in a 21700 format.
E-Bike / Mobility
- Useful for performance-oriented packs with proper parallel count.
- BMS and thermal validation are required.
RC / Robotics
- Appropriate for motor-driven platforms requiring compact high discharge.
- Monitor temperature under burst-heavy duty cycles.
High-Output Lighting
- Suitable for 21700-compatible lights that need high current.
- Verify driver current and physical fit.
Custom Packs
- Useful for advanced builders working with spot welding and pack validation.
- Requires matched cells and proper insulation.
Energy Storage
- Works where higher current is needed.
- For maximum runtime alone, consider higher-capacity energy cells.
17. Selection Bias: Power vs. Runtime
for shoppers comparing high-power and high-energy 21700 cells.
18. Application Suitability Matrix
Simple product-page fit guidance.
| Power tools | Strong fit |
|---|---|
| Robotics / RC | Strong fit |
| High-output flashlights | Strong fit |
| Performance mobility packs | Validate thermally |
| Max runtime per cell | Consider 5000mAh-class cells |
| Unmanaged consumer devices | Not recommended |
Safety, Handling & Compatibility Notice
This product is an unprotected lithium-ion cell. It should only be used by customers who understand cell-level lithium-ion safety and who are using the battery in compatible hardware, managed packs, or professionally designed assemblies. Improper use can lead to overheating, venting, fire, or explosion.
- Charge only with lithium-ion chargers or managed battery systems designed for the correct chemistry and cell count.
- Never short circuit, crush, puncture, incinerate, or expose the cell to water.
- Do not use cells with damaged wraps, dented cans, or missing top insulator rings.
- Do not mix with cells of different age, capacity, model, or state of charge in the same pack.
- For assembly, use spot welding rather than direct soldering to reduce heat damage risk.
- Store and transport in non-conductive cases; never carry loose cells in pockets or bags.
- Keep away from children and from applications for which the product is not specified.
- Not for e-cigarette, vape, or similar use.
Common technical questions about the Samsung 40T.
What is the capacity of the Samsung 40T?
The abridged Samsung specification lists minimum standard discharge capacity of 4000mAh and minimum rated discharge capacity of 3900mAh.
What is the continuous discharge rating?
Use 35A as the primary continuous-discharge rating. Samsung also lists 45A with an 80°C surface-temperature cut, which requires thermal protection and should not be presented as an unrestricted rating.
Is this a protected battery?
No. This is an unprotected flat-top 21700 cell and should only be used in devices or packs with suitable over-charge, over-discharge, over-current, short-circuit, and temperature protection.
What charger should be used?
Use a lithium-ion charger or managed battery system with a 4.20V CC-CV profile. The Samsung reference standard charge is 2A, while the rated charge is 6A.
What is the discharge cut-off voltage?
The discharge cut-off is 2.5V per cell. A finished device or BMS may use a higher cut-off to improve service life or add safety margin.
Can the Samsung 40T be used in battery packs?
Yes, but pack builds require matched cells, spot welding, proper insulation, fusing or current-path design, BMS protection, thermal monitoring, and validation at the real load profile.
Can I solder wires directly to this cell?
Direct soldering is not recommended. Spot welding is the preferred assembly method because it reduces the risk of overheating the cell.
What are the cell dimensions?
The Samsung outline drawing lists 21.22mm maximum diameter and 70.30mm maximum height, with tube included. The live listing gives approximate retail dimensions of 21.4mm × 70.0mm.
What temperature range is allowed?
The abridged specification lists ambient charge of 0°C to 45°C and ambient discharge of -20°C to 60°C. The surface-temperature section lists charge of 0°C to 50°C and discharge of -20°C to 80°C, with recommended release thresholds.
What is the cycle-life criterion?
Samsung lists a criterion of at least 2400mAh after 250 cycles using 6A charge and 35A discharge to 2.5V at 25°C. Actual cycle life depends on current, temperature, cut-off voltage, charge method, and pack design.
Is this better for power or runtime?
The 40T is a balanced high-power 21700 cell. It offers more runtime than many lower-capacity power cells and more current capability than many higher-capacity energy cells.
Can I carry this battery loose?
No. Loose transport is unsafe because metal objects can short the terminals. Always use a non-conductive battery case.