LiPo vs LiFePO4 vs Supercapacitor Jump Starters: Which Is Safest?

Many portable jump starters use the same kind of lithium battery as a mobile phone, and many of them spend their lives in a car's boot or glovebox. In an Australian summer that is a harsh place for a battery. This guide compares the three technologies you will find in jump starters (LiPo, LiFePO4 and supercapacitor) and explains why we have chosen to sell only LiFePO4 and supercapacitor models. It also covers the real trade-offs between each technology.

The Three Jump Starter Technologies

LiPo and Other Cobalt/Nickel Lithium-Ion Jump Starters

In this guide, "LiPo" means jump starters built with lithium-polymer or lithium-ion cells that use cobalt- or nickel-based cathodes, such as lithium cobalt oxide (LCO) or nickel manganese cobalt (NMC). These chemistries pack a lot of energy into a small, light cell (about 150–220 Wh/kg), which is why LiPo jump starters are compact and usually the cheapest option.

The trade-off is heat tolerance and life span. Battery University lists a typical cell-level thermal runaway temperature of about 150°C for LCO and 210°C for NMC, and a cycle life of 500–1,000 cycles for LCO and 1,000–2,000 for NMC. Research on cathode chemistry also shows that the more nickel a layered cathode contains, the lower the temperature at which it starts to break down and the more oxygen it releases, and that oxygen feeds a fire inside the cell.

LiFePO4 (Lithium Iron Phosphate) Jump Starters

LiFePO4 (also called LFP or lithium iron phosphate) is still a lithium battery, but its phosphate cathode is held together by a strong phosphorus-oxygen bond, giving it better thermal stability than layered cobalt and nickel oxide cathodes. Battery University describes it as "one of the safest Li-ions" and a "very safe battery even if fully charged", with a typical cell-level thermal runaway temperature of about 270°C and a cycle life of 2,000 cycles or more. In mechanical abuse testing by Sandia and Oak Ridge National Laboratories, the lithium cobalt oxide cells tested were more prone to thermal runaway than the LFP cells tested.

LiFePO4 is not fireproof. Any lithium cell can still fail if it is crushed, overcharged or badly overheated, so a LiFePO4 jump starter still needs a good battery management system and sensible storage. It is also heavier and bulkier than LiPo for the same stored energy (about 90–120 Wh/kg) and usually costs more.

Supercapacitor ("Batteryless") Jump Starters

A supercapacitor (also called an ultracapacitor or EDLC) stores energy as an electric charge on the surface of its electrodes rather than through a chemical reaction. This brings three big advantages:

• Very low stored energy: a typical supercapacitor holds about 5 Wh/kg, compared with 120–240 Wh/kg for lithium-ion. If something does go wrong, there is far less energy to release.
• Extremely long life: around 1 million charge cycles, with capacity typically fading only from 100% to 80% over 10 years.
• Wide temperature range: supercapacitors are typically rated to charge and discharge from –40°C to 65°C, while lithium-ion is typically limited to 0–45°C for charging and –20–60°C for discharging.

Because the energy is stored physically, with no chemical reaction involved, a supercapacitor has no chemical thermal runaway. That is why we regard supercapacitors as the safest jump starter technology available. Safest does not mean perfect, though. A supercapacitor can still be damaged if it is charged above its rated voltage, and the downsides below are real.

The Honest Drawbacks of Supercapacitor Jump Starters

• They don't hold their charge for long. A supercapacitor self-discharges much faster than a battery. It falls from 100% to about 50% in 30–40 days, while lithium batteries lose about 5% a month. Most supercapacitor jump starters are designed to be charged just before you use them, not kept charged in the boot for months.
• They need some energy to start with, but very little. This drawback is also one of their biggest advantages. A flat car battery usually still holds plenty of energy; it just can't deliver the huge current needed to crank the engine. A supercapacitor needs so little energy that it can recharge from that same flat battery in a few minutes, or from a 12V socket or USB power bank (check each model's specifications), and then release it as a very large burst of current. The current a capacitor can take in or deliver depends on how quickly its voltage changes (I = C × dV/dt), so it can charge quickly and discharge enormous current over a few seconds. If the battery is completely dead or disconnected, you will need another source of power to charge the jump starter first.
• Low energy means limited extras. Because a supercapacitor stores so little energy, it is built to crank an engine, not to charge phones or run accessories for hours.
• Voltage falls as they discharge. A supercapacitor's voltage drops steadily as it empties, unlike a battery's flat discharge curve, so it delivers its best cranking performance in the first attempt or two after a full charge.
• Higher cost, size and weight. Supercapacitors cost far more per unit of stored energy than lithium batteries. Expect to pay more, and expect a larger, heavier unit than a LiPo jump starter with a similar rating.

Comparison Table

The Hot Car Problem in Australia

A parked car heats up fast. Kidsafe Queensland reports that the inside of a car can be 30–40°C hotter than outside, so on a 30°C day the cabin can reach about 70°C, with 75% of the rise in the first 5 minutes. Opening the windows 5 cm only drops the peak slightly (78°C closed versus 70°C with windows open). RACV testing found interiors can pass 70°C within minutes when it is only 30°C outside, and the NRMA warns that a parked car can be more than 30°C hotter than the outside temperature.

Those temperatures are above the typical rated limits of lithium-ion batteries. The ACCC's product safety advice is clear: don't leave lithium-ion batteries or products in hot places such as in parked vehicles. Fire and Rescue NSW reported at least 318 lithium-ion battery fires in NSW in 2024, up from 272 in 2023 and 165 in 2022.

Jump starters have been part of this problem. Lithium-ion jump starters have been recalled in Australia and overseas after reports of overheating and fires, including units that overheated when stored in high temperatures.

Even a closed car can exceed a supercapacitor's typical 65°C rating, so no jump starter should be left baking on the dashboard. The difference is what happens when things go wrong. A supercapacitor holds very little energy and has no chemical thermal runaway, and a LiFePO4 cell is far more resistant to runaway than a LiPo cell. That is a much safer position to be in than carrying a compact high-energy LiPo pack through an Australian summer.

Peak Amps, Cranking and Cold Starts

Jump starters are usually sold on "peak amps". This is a figure each manufacturer rates for its own product, so treat it as a rough guide rather than a like-for-like comparison between brands. Look at the engine size and fuel type the manufacturer says the unit is designed for, and for diesels and large petrol engines leave yourself some headroom.

In the cold, batteries struggle more than supercapacitors. Supercapacitors are rated to work down to about –40°C, and lithium-ion is typically rated to –20°C for discharge and should not be charged below 0°C. For most of Australia, heat is the bigger concern, but the cold matters if you travel to the high country or inland in winter.

Why We Only Sell LiFePO4 and Supercapacitor Jump Starters

Our customers keep jump starters in caravans, motorhomes, 4WDs, utes and boats, often in direct sun and for months at a time. We think a cheap LiPo jump starter is the wrong product for that life. LiPo chemistries have lower thermal runaway temperatures and shorter cycle lives than LiFePO4, lithium-ion jump starters have been recalled for overheating, and the ACCC advises against leaving lithium-ion products in parked vehicles. So we have chosen to sell only:

• LiFePO4 jump starters: our pick if you want a unit that stays charged for months, can also power accessories, and is much more thermally stable than LiPo.
• Supercapacitor jump starters: our pick for the highest level of safety and the longest life, if you are happy to charge the unit just before use and don't need it as a power bank.

Which One Should You Choose?

• Choose LiFePO4 if you want a grab-and-go jump starter that holds its charge for months, can charge phones or run a compressor, and is lighter and cheaper than a supercapacitor unit with a similar rating.
• Choose supercapacitor if safety and life span matter most, the unit will live in a hot vehicle year-round, and you are comfortable charging it from the car's weak battery, a 12V socket or a USB power bank before each use.
• Avoid LiPo for a jump starter that travels with you. If a jump starter has to live in a vehicle through an Australian summer, a supercapacitor unit is the best choice. LiFePO4 is far more thermally stable than LiPo, but like any lithium battery it should not be left in a hot parked car; keep it out of direct sun and within the manufacturer's rated storage temperature.

Whichever you choose, store it out of direct sunlight, follow the manufacturer's charging and storage instructions, and stop using any lithium jump starter that is swollen, damaged or has been exposed to extreme heat.

Sources

1. Battery University (Cadex Electronics), BU-205: Types of Lithium-ion
2. Investigating the critical characteristics of thermal runaway process for LiFePO4/graphite batteries by a ceased segmented method, iScience (2021), doi 10.1016/j.isci.2021.103088, via PubMed Central
3. Sandia National Laboratories and Oak Ridge National Laboratory, Li-ion Batteries Thermal Runaway Risk Grading and Prediction (2024)
4. Battery University (Cadex Electronics), BU-209: How does a Supercapacitor Work?
5. US Department of Energy, Technology Strategy Assessment: Supercapacitors (July 2023)
6. Kidsafe Queensland, Hot Cars fact sheet
7. RACV, How to keep your car cool in summer and stay safe
8. NRMA, Fresh warning for parents leaving children unattended in cars (18 December 2025)
9. ACCC Product Safety Australia, Lithium-ion batteries guide
10. Fire and Rescue NSW / NSW EPA, Spate of lithium-ion fires and NSW Government survey sparks community wakeup call on battery risks (10 February 2025)