Li-Ion Battery

5 04 2014

Your iOS device gets its energy from a Li-Ion battery.
Li is the symbol of Lithium discovered in 1817, weighs about o.5 g/cm3, and melts at about 180C (360F). It is a soft silver-white metal, the lightest metal, and as all alkali metals it’s highly reactive and flammable. Lithium mine production is mainly done in Chile, Australia, China, and Argentina. Due to its high reactivity it does not naturally occur in elemental form.

Lithium is corrosive and requires special handling to avoid skin contact. Breathing Lithium dust or compounds initially irritates nose and throat. Carriage and shipment of some kinds of Lithium batteries may be prohibited aboard certain types of transportation (aircraft) because of

the ability of most types of lithium batteries to fully discharge rapidly when short-circuited leading to overheating and possible explosion in a process called thermal runaway.

A thermal runaway is not very common (just two or three battery packs per million burst into flames) but when it happens, it’s extreme. In some situations, the failure rate can rise, and when that happens you end up with a worldwide battery recall that can cost manufacturers millions of dollars.

But don’t worry, batteries in your iOS device have thermal overload protection.


The specific energy density of Li-Ion batteries is 100 to 250 Wh/kg (o.47$/Wh) and so it’s only comparable with Alkaline long-life batteries 0.19$/Wh). Because of the increasing usage in the automobile industry costs will decrease down to 0.20$/Wh in the near future.

Li-Ion batteries have a self-discharge rate of approximately 5–10% per month, compared to over 30% per month in common nickel metal hydride batteries, approximately 1.25% per month for low self-discharge NiMH batteries and 10% per month in nickel-cadmium batteries.

The electrical charge …

In tech specs you find the physical unit Milliamps Hour (mAh). It characterizes the ‘strength’ (the right physical term is ‘charge’) of a battery. The higher the mAh, the longer the battery will last.

Milliamps Hour is 1/1000th of an Amp Hour, so a 1000mAh = 1.0Ah

Think of it as a car’s gas tank. Voltage is how much gas is being used, and mAh is the size of the gas tank. The bigger the gas tank (mAh) rating the longer the device will run. If your battery is rechargeable, then think of the gas tank as refillable (rechargeable).

In physics an ampere-hour or amp-hour (symbol A·h, A h, Ah) is a unit of electric charge, with sub-units milliampere-hour (mA·h or mAh; often used in rechargeable and disposable battery specifications) and milliampere-second (mA·s). One ampere-hour is equal to 3600 Coulomb, the unit for electrical charge. The commonly seen milliampere-hour (mA·h or mAh) is one-thousandth of an ampere-hour (3.6 Coulomb).

Basics …

Get familiar with some physical units to understand the calculation.

  • Volt
    unit of electrical potential or motive force
    Potential is required to send one ampere of current through one ohm of resistance
  • Ampere
    unit of current
    One ampere is the current which one volt can send through a resistance of one ohm
  • Watt
    unit of electrical power
    Power is energy per time.
    One watt is the product of one ampere and one volt – one ampere of current flowing under the force of one volt gives one watt of power
  • Coulomb
    unit of electrical charge
    One Coulomb is transported if a current of one Ampere flows through a conductor for one second.
    It is equal to the charge of approximately 6.241×10 to the power of 18 electrons (6,241,000,000,000,000,000).
    So you can see that your investment in an iPhone is accompanied by a significant countervalue.
  • Joule
    unit of energy
    One Joule is one watt (power) being effective for one second. The unit is named after the UK physicist James Prescott Joule.

Electrical energy is potential energy before it is delivered to the end-use. Once converted from potential energy, electrical energy can always be described as another type of energy (heat, light, motion, etc.). In case of your iPhone most of the energy is used to enlighten the touchscreen and connecting to the outer world, aka internet.

Energy stored in your iPhone …

With these basics and Apple’s tech specs for the iPhone 5S we now can calculate the energy stored in the Li-Ion polymer battery.

Energy = Power x Time

The battery of the iPhone 5S has a electric charge of 1510 mAh (1.51 Coulomb) and works on 3.8 volts.

So the electrical energy stored in the battery is

1.51 A x 3,600 sec x 3.8 V = 20,656.8 J

that means approximately 21 kJ (kilo Joule).

In reality this calculation is not fully correct because the voltage varies.

One Joule in everyday life represents approximately:

  • the energy required to lift a small apple (with a mass of approximately 100 g) vertically through one meter
  • the kinetic energy released when that same apple falls one meter to the ground.

So your fully charged iPhone approximately offers the energy released when 21,000 apples fall one meter to the ground.


As an Apple fan you might feel sad with these many crashes of apples so just replace apples by bars of chocolate.

Safety …

Lithium-Ion batteries can be dangerous under some conditions and can pose a safety hazard since they contain, unlike other rechargeable batteries, a flammable electrolyte and are also kept pressurized. This makes the standards of these batteries high, and it consists of many safety features. There have been many reported accidents as well as recalls done by some companies.

Reducing energy consumption

Follow the instructions in this mind map to reduce energy consumption of your iOS device.


Feel free to download this map from my Box account.

The alternative file formats have been created with iThoughts HD for iPad (.ITMZ file format). Compatibility to other tools is limited. The DOCX file format is suggested for those who don’t use a mind mapping tool. The file contains the image as well as a detailed outline of all topics.

Application File format
Adobe Reader PDF
Apple iWork/Microsoft Word DOCX
iThoughts ITMZ
MindManager MMAP

Summary …

There is much energy stored in a fully charged iOS device but it’s still not enough to cover a whole day of frequent usage. With larger form factors for the iPhone battery life might be improved. There are already some innovative features in Apple’s operating system to reduce energy consumption up to the user behavior. The target however should be a 12h usage or, more convenient, an energy equivalent of 42,000 apples.

Related links …

What is electrical energy?

Li-Ion safety concerns

Apple about iPhone batteries

Thanks for stopping by and charging your brain.



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