Cold weather can significantly change how a jump starter battery performs. As temperature falls, usable capacity, voltage behavior and high-current capability can all change, while the engine itself may require more current to crank.
For this reason, evaluating a cold-weather jump starter requires more than checking the peak-current number printed on the product.
BoltPower R&D evaluated jointly developed sodium-ion cells and selected NMC lithium-ion cells under several low-temperature conditions. Testing included 10C discharge at -10°C and 1C discharge at -20°C and -40°C.
The results show a clear difference in how the tested cell groups retained capacity as temperature decreased. They also show why low-temperature cell capacity should not be confused with actual vehicle cold-cranking performance.
Key Takeaways
- In BoltPower’s earlier -10°C / 10C test, the tested sodium-ion cells retained around 91% of reference capacity in both capacity groups. Full sample data and discharge curves are presented in our main sodium-ion jump starter test article.
- At -20°C / 1C, the tested sodium-ion cells retained approximately 88–93% of their 25°C capacity, compared with approximately 72–74% for the tested NMC cells.
- At -40°C / 1C, the tested sodium-ion cells retained approximately 86–88% of their 25°C capacity, compared with approximately 22–23% for the tested NMC cells.
- Capacity retention and energy retention are not the same. At -40°C, the tested sodium-ion cells retained about 69–73% of their 25°C energy, lower than their capacity-retention percentages.
- These results are cell-level discharge results, not proof that a complete jump starter can crank a vehicle at -40°C.
Recent industry research also identifies low-temperature performance as an important area for sodium-ion development, while emphasizing that cell chemistry, electrolyte design and interfaces still strongly influence actual performance. The IEA likewise notes that sodium-ion is entering a scale-up phase but remains constrained by lower energy density than lithium-ion technologies.
Why Cold Weather Is Challenging for a Jump Starter Battery
A jump starter has a very different duty cycle from an ordinary rechargeable device.
A power bank may supply a relatively small amount of current over several hours. A jump starter has to provide a much larger current within a very short period when the engine is cranked.
Low temperature makes that job harder.
As battery temperature falls, electrochemical reaction rates slow and internal resistance can increase. Available capacity, voltage under load and rate capability may therefore decline. At the same time, cold engine oil and other mechanical factors can increase the current required to crank an engine.
This creates two simultaneous requirements:
the battery has to perform under more difficult conditions while the vehicle may be asking more from it.
That is why a statement such as:
“Operating temperature: -40°C”
does not by itself tell a buyer whether a jump starter will actually perform well in extreme cold.
The test method matters.
How BoltPower Evaluated Low-Temperature Cell Performance
BoltPower R&D compared two cell-capacity groups:
| Cell Group | Sodium-Ion | NMC |
| Group A | 2.0Ah | 2.0Ah |
| Group B | 2.5Ah | 2.5Ah |
Internal cell model numbers and development-partner information are not disclosed.
Because sodium-ion and NMC cells have different electrochemical voltage characteristics, the two chemistries were evaluated using their respective specified voltage ranges:
- Sodium-ion: 1.5–3.95V
- NMC: 2.8–4.2V
This is important when interpreting the data. The tests used comparable SOC, temperature and discharge-rate frameworks, but the two chemistries were not forced to use the same absolute cutoff voltage.
For the extreme-temperature comparison, cells were charged at 25°C, conditioned at the target low temperature for 12 hours, and then discharged at 1C. Results were compared with each cell group’s own 25°C reference performance.
This normalization allows the question to be framed correctly:
How much of its own room-temperature performance did each tested cell retain when temperature decreased?
What the Earlier -10°C Test Showed
Before moving to the more extreme temperatures, BoltPower also evaluated the cells at -10°C under a 10C discharge rate.
The tested sodium-ion groups retained approximately 91% of their reference capacity. The NMC results varied by cell group, with the 2.5Ah group showing a smaller difference than the 2.0Ah group.
We do not repeat the four detailed -10°C charts here.
The complete individual-sample capacity-retention data and 10C discharge profiles are available in:
Sodium-Ion Jump Starters: How They Work, Benefits and Real Test Data
The important point for this article is that -10°C provides the first stage of the temperature picture.
As the temperature was reduced further to -20°C and -40°C, the differences between the tested cell platforms became much more pronounced.
What Happened at -20°C?
At -20°C, cells were discharged at 1C after 12 hours of temperature conditioning.
The result was measured as capacity retention relative to the corresponding 25°C test.
Capacity Retention at -20°C
| Cell Group | Sodium-Ion | NMC |
| 2.0Ah | 88.2% | 72.4% |
| 2.5Ah | 92.7% | 74.2% |
For the 2.0Ah group, the tested sodium-ion cells retained approximately 88.2% of their 25°C capacity. The tested NMC cells retained approximately 72.4%.
For the 2.5Ah group, sodium-ion capacity retention was approximately 92.7%, compared with approximately 74.2% for NMC.
Under these specific test conditions, both sodium-ion groups therefore retained a larger proportion of their own room-temperature capacity.
However, this should not be interpreted as a universal sodium-ion-versus-NMC result. Cell formulation, electrode materials, electrolyte, internal resistance and construction can all affect low-temperature behavior.
What Changed at -40°C?
At -40°C, the same 1C comparison showed a much larger difference.
Capacity Retention at -40°C
| Cell Group | Sodium-Ion | NMC |
| 2.0Ah | 86.0% | 22.4% |
| 2.5Ah | 87.7% | 23.4% |
The tested 2.0Ah sodium-ion cells retained approximately 86.0% of their 25°C capacity, while the NMC group retained approximately 22.4%.
For the 2.5Ah group, sodium-ion retained approximately 87.7%, compared with approximately 23.4% for the tested NMC cells.
The significance of this result is not simply that one bar is higher than another.
The more useful observation is that, within these tested cell groups:
the sodium-ion cells showed relatively limited capacity loss between -20°C and -40°C, while the tested NMC cells showed a much larger decline at -40°C.
This makes extreme-low-temperature behavior particularly relevant when evaluating battery platforms for products intended for cold-climate markets.
Industry research supports the broader point that low-temperature sodium-ion performance can be promising, but it also cautions against treating all sodium-ion chemistries as equivalent. Low-temperature ion transport, electrode structure and electrolyte behavior remain important technical constraints.
Low-Temperature Capacity Retention Comparison
The charts below summarize the capacity-retention results at both -20°C and -40°C for the tested 2.0Ah and 2.5Ah cell groups.
Figure 1: Sodium-Ion vs NMC Capacity Retention at -20°C and -40°C — 2.0Ah
Figure 2: Sodium-Ion vs NMC Capacity Retention at -20°C and -40°C — 2.5Ah
The comparison shows that the difference between the tested sodium-ion and NMC cells became much more pronounced at -40°C than at -20°C.
Capacity Retention Is Only Part of the Story
A battery can retain a high percentage of its Ah capacity while still losing more of its usable energy.
That is because:
Capacity measures charge in Ah, while energy in Wh also depends on voltage.
This matters when comparing different battery chemistries and when evaluating performance at very low temperatures.
BoltPower therefore also reviewed energy retention relative to 25°C.
Energy Retention at -20°C and -40°C
| Temperature | Sodium-Ion 2.0Ah | NMC 2.0Ah | Sodium-Ion 2.5Ah | NMC 2.5Ah |
| -20°C | 73.7% | 65.6% | 85.2% | 66.6% |
| -40°C | 69.3% | 17.7% | 72.9% | 18.5% |
At -40°C, for example, the sodium-ion groups retained approximately 86–88% of their 25°C capacity, but approximately 69–73% of their 25°C energy.
That difference is important.
It indicates that voltage behavior still deteriorated as temperature fell, even though much of the measured Ah capacity remained available.
For a technical buyer, this is a better interpretation than simply saying:
“The battery keeps 87% capacity at -40°C.”
A more complete statement is:
The tested sodium-ion cells retained approximately 86–88% of their 25°C capacity and approximately 69–73% of their 25°C energy at -40°C under 1C discharge.
Does 87% Capacity Retention at -40°C Mean a Jump Starter Can Start a Car at -40°C?
No.
This is probably the most important distinction in the entire article.
The -20°C and -40°C results above were measured using 1C cell-level discharge tests.
Engine starting requires a much higher short-duration current.
A complete cold-weather jump start depends on more than cell capacity, including:
- cell pulse-discharge capability;
- pack configuration;
- internal resistance;
- BMS and switching components;
- clamp and cable resistance;
- connection quality;
- vehicle battery condition;
- engine displacement;
- crank duration;
- complete-product temperature.
Therefore:
Supported conclusion
The tested sodium-ion cells retained 86–88% of their 25°C capacity at -40°C under a 1C cell-level discharge test.
Not supported by this test alone
A complete jump starter can start any vehicle at -40°C.
Those are two different claims.
For OEM/ODM buyers, asking a supplier what type of -40°C test was actually performed is therefore more useful than simply asking whether the product “supports -40°C.”
Four Different “Cold-Weather” Claims Buyers Should Not Confuse
This is especially important in B2B sourcing because similar temperature numbers can describe very different tests.
1. Storage Temperature
The product or battery can be stored at a specified temperature.
This says nothing by itself about whether it can deliver starting current at that temperature.
2. Cell Discharge Temperature
An individual cell can discharge under a defined current and cutoff condition.
This is the type of evidence represented by the -20°C and -40°C 1C data in this article.
3. High-Rate Low-Temperature Discharge
The cell is tested at a substantially higher discharge rate.
BoltPower’s earlier -10°C / 10C testing belongs to this category.
4. Complete Vehicle Cold-Start Test
A finished jump starter is used to crank a defined engine under specified low-temperature conditions.
This is the closest of the four to real product use.
These tests are related, but they are not interchangeable.
A procurement specification should state which one is required.
Why Lithium-Ion Still Matters
The low-temperature results above should not be used to conclude that NMC or lithium-ion is an inferior battery technology.
Lithium-ion remains the mainstream platform for portable jump starters for important reasons.
One of the biggest is energy density.
For a given stored energy requirement, higher energy density can help produce a smaller and lighter product. Lithium-ion also benefits from mature manufacturing processes, a large supplier ecosystem, established pack design experience and broad commercial adoption.
The IEA notes that sodium-ion technology is now entering a scale-up phase, but lower energy density remains one of its key constraints relative to lithium-ion technologies.
For a compact jump starter where size and weight are major product priorities, those lithium-ion advantages remain valuable.
Sodium-ion therefore should not be positioned as:
the replacement for lithium-ion.
A better engineering interpretation is:
Sodium-ion provides another battery-platform option when the target application’s priorities justify a different trade-off between low-temperature behavior, high-rate performance, energy density, size and commercial maturity.
That is also how BoltPower approaches the technology.
What These Results Mean for Cold-Weather Jump Starter Design
Selecting a battery chemistry is only the beginning.
A cold-weather jump starter has to be engineered as a complete system.
For example, strong cell-level low-temperature performance can still be undermined by excessive resistance in:
- internal pack connections;
- MOSFETs;
- cables;
- clamps;
- connectors.
Likewise, peak-current numbers are only useful when the battery can maintain adequate voltage for the required crank period.
This is why BoltPower’s evaluation process looks at battery behavior in the context of a jump-starting application rather than relying on a single battery specification.
For B2B product development, the target requirement should therefore start with questions such as:
What is the target climate?
What engines must the product support?
What starting-current requirement is needed?
What size and weight limits apply?
How long is the expected storage period?
What complete-product validation is required?
Only then does battery chemistry selection make sense.
How Does This Relate to the BoltPower K29N?
BoltPower has applied sodium-ion technology to the K29N Sodium-Ion Jump Starter.
K29N Key Specifications
| Specification | K29N |
| Battery technology | Sodium-Ion |
| Battery energy | 30Wh |
| Starting current | 500A |
| Peak current | 1000A |
| USB-C input | 5V/3A, 9V/2A |
| USB-A output | 5V/2.4A |
The K29N is a practical application of BoltPower’s sodium-ion jump-starter development work.
However, the cell-level -20°C and -40°C results in this article should not automatically be interpreted as complete K29N cold-cranking specifications.
Cell validation and finished-product validation are separate stages.
For complete model specifications:
For the wider technology overview, including BoltPower’s 150C pulse testing, -10°C / 10C testing, storage and cell-level safety data:
Sodium-Ion Jump Starters: How They Work, Benefits and Real Test Data
What Should a B2B Buyer Ask Before Sourcing a Cold-Weather Jump Starter?
For distributors, automotive brands and sourcing teams, a low-temperature claim should be backed by a defined test method.
Before comparing two products, ask:
- What temperature was tested?
- How long was the battery conditioned at that temperature?
- What was the SOC before testing?
- Was it a cell, battery pack or complete jump starter?
- What discharge rate or current was used?
- What cutoff condition was applied?
- Was the result capacity retention, pulse output or actual engine starting?
- What engine type and displacement were used for vehicle testing?
- Was the product itself cold-soaked before the starting test?
A specification such as:
“-40°C operating temperature”
is far less informative than:
“-40°C, 12-hour conditioning, 1C cell discharge, capacity retained relative to 25°C baseline.”
For B2B procurement, test definition is often as important as the headline number.
So, Is Sodium-Ion Better for Cold-Weather Jump Starters?
The answer depends on what “better” means.
In BoltPower’s tested cell groups, sodium-ion retained substantially more capacity and energy than the selected NMC cells at -40°C under the specified 1C test conditions.
That is a meaningful result for battery-platform evaluation.
It does not prove that every sodium-ion cell will outperform every lithium-ion cell, and it does not mean that a finished sodium-ion jump starter automatically has superior cold-cranking performance.
Lithium-ion continues to offer strong advantages in energy density, compactness, supply-chain maturity and commercial scale.
Sodium-ion adds another engineering option—particularly worth evaluating when low-temperature performance and high-current operation are important design requirements.
For BoltPower, the objective is therefore not to replace lithium-ion across the jump-starter range.
It is to understand where each battery platform fits the target market and develop the product around that requirement.
Test Data Note
The test results presented in this article come from cell-level testing conducted by the BoltPower R&D team using jointly developed sodium-ion cells and selected NMC comparison cells.
Internal cell model numbers and development-partner information are not disclosed.
Unless otherwise stated:
- capacity and energy retention values are relative to each cell group’s own 25°C reference;
- sodium-ion and NMC cells were evaluated using chemistry-appropriate voltage limits;
- reported values represent the specific samples and test conditions evaluated by BoltPower.
These results should not be generalized to all sodium-ion or NMC cells and should not be treated as complete-product or vehicle cold-cranking specifications.