I was looking at the details of this jumpstart product:

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It claims to be 2 lbs and 14.2 x 12 x 3.5 inches, which I think is for the outer black canvas case, so I would guess the actual device is less than 9.5 x 5.5 x 3 inches. I assume this is a Li-Ion battery.

Conversely, a standard lead-acid battery for a common small car is 9.4 x 5.1 x 8.8 inches - 3 times as big, and maybe 10 times as heavy (This is BCI form factor 51R which is used by the 2015 Honda Civic).

I assume the different battery chemistry accounts for the smaller size of the jumpstarter.

Why do modern cars not use this smaller battery type? Looking at the amazon link it doesn't seem to be a matter of cost - the jumpstarter price is in a similar ballpark to what one would pay for the 51R lead-acid battery.

4 Answers 4


The two biggest disadvantage of lead acid batteries compared to the newer types like Li Ion are that they are heavier, and that they contain liquid acid. Another possible issue is that they can produce hydrogen gas.

On the other hand, they are very inexpensive, have a long life expectancy, have a very high tolerance for overcharging without being damaged, and they hold a charge longer than other types. They are also able to handle high discharge rates. Here are some comparison charts

Looking at the disadvantages, you can see that they're mostly irrelevant in a car. The weight of the battery is trivial compared to the weight of the rest of the components.

Being able to stand long periods of slow charging without damage, and being able to sit unused for long periods of time without losing charge are ideal properties for a car battery.

Being light weight and packing a lot of energy into a small package are just not that important for a car, but they're critical for portable devices, and this jump starter is in fact a portable device.

Looking at the cost of this jump starter and comparing it to the cost of a lead acid battery is not really realistic, because this device would not be able to start your car daily for years without failing. You'd be replacing it much more frequently.

That said, it's definitely true that newer battery technologies are showing up in cars, especially hybrids and electric vehicles. But those don't need jump starts, and for most ICEs, the lead-acid battery still provides the most reliable and durable option.

  • Correct - the discharge rate is the showstopper feature of lead-acid batteries. They can dump a lot of current quickly, without being damaged. This is required to spin a big heavy cold motor-lump. Other batteries can't achieve the same discharge rates without added complexity.
    – Criggie
    Jan 1, 2017 at 0:41
  • I think that normal ICE cars might go to lithium some time in the future . I have seen after market Lithium batteries manufactured for trail bikes .4 cells seems to be the option from what little I have seen .For me this means that all future Automotive stuff like Radios Voltage droppers Turbo timers should be Able to operate on up to 16.8 VDC .
    – Autistic
    Feb 6, 2017 at 6:07

I have seen "jump starters" like this everywhere. I was given one to evaluate by an Autoelectric importer. I thought it was rubbish. I warned him and he didn't import them.

How they work is by using a battery that has very good power density, but poor energy density .Its like being very strong but not fit.The batteries that are used are Nicad and its environmentally friendly cousin, the nickel metal hydride. The lithium battery is a good all rounder when it comes to energy density and power density, but it costs much more so you tend not to see them used for jump starting. If you tried to put say a nicad in a normal car the charging system would need to be different and you would find that flat battery syndrome would occur more often. This is because of the increased self discharge rate and the smaller amp hours due to the much smaller size.


The jump-start battery can't store enough energy to run the car

Unlike jump-starting kits, car batteries are not just used for cranking the engine; they serve as an energy storage unit for virtually all electrical sub-systems (lights, coils, injectors, ECU, power windows, power seats, radio, cooling fans, miscellaneous sensors, etc.).

The product in question is designed to store 15 Ah worth of energy. This is not enough to meet the energy demand of all vehicle sub-systems.

Here are some Ah ratings of batteries for a few vehicles:

  • Toyota Corolla, 41 Ah
  • Pontiac GTO, 70 Ah
  • VW Touareg, 110 Ah
  • 1
    Technically, ampere hours are units of charge, not energy.
    – barbecue
    Sep 5, 2015 at 1:49
  • 1
    Right, but as long as we're talking about a common voltage when comparing Ah ratings they should indicate energy storage as well.
    – Zaid
    Feb 19, 2016 at 13:11
  • I was just being nit-picky.
    – barbecue
    Feb 19, 2016 at 17:01
  • 2
    This answer is wrong. A car battery does not "run" the car. It only starts the engine. Once the engine runs, all power needs are served by car's alternator. You can run a car with dead battery forever if you don't stop the engine. The portable starters do work, used them myself (Black&Decker Smart charger, 75A engine start). The question remains open. The answer by "Autistic" is likely correct, but I'd like to see some electrical engineering level of explanation. Dec 31, 2016 at 4:24
  • 2
    @AliChen do you have a particular make/model/year in mind when you say that a battery is not needed? The old-school, carbureted vehicles can be made to run without a battery, but I can tell you from experience that a fuel-injected vehicle with a non-charging alternator (or alternator belt removed) will remain alive for a short period of time (until the battery runs flat). Usually, the alternator serves to charge the battery, not deliver power the electrics directly.
    – Zaid
    Dec 31, 2016 at 8:22

Though the question might seem absurd to many people, I think it is quite a common question; because a small battery would be more convenient but yet, car batteries are usually large. Look! The car battery has to keep activated many devices that a car has; like, fan, light, music and if you take some more devices in the car, the only battery has to provide all power; which requires it to have more storages and the battery becomes large. However, Li lon batteries are more convenient than the liquid acid based batteries. In the future, we expect to have a comparatively smaller battery for cars. Thank you.

  • what do you mean by "storages" ? Please use standard definitions so we are all clear what is being discussed.
    – Solar Mike
    Jan 6, 2019 at 10:28

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