Batteries help power a plethora of portable electrical and electronic devices such as watches, smartphones, laptops, remote control devices, and so much more.
The world is filled with many variations of battery each having its own unique characteristics.
One of the most common batteries used nowadays is Lithium-Ion.
Sooner or later, the Lithium-Ion is going to go dead (lose all its charge), and if it is a rechargeable battery, will need to be recharged.
Letting a battery go fully dead is not an ideal situation, so knowing at what voltage a Lithium-Ion battery loses all its charge will help you extend its lifespan.
So, at what voltage is a Lithium-Ion battery considered dead? The voltage at which a Lithium-Ion is dead is around 3.4 volts. This voltage can vary depending on factors such as the temperature and also its manufacturer. Lithium-Ion batteries should not be used when they are dead. They contain a cutoff circuit to protect them from being used past the voltage at which they have lost all its charge.
This article shall take a look closer at Lithium-Ion batteries and its discharge profile.
Deeper look at a Lithium-Ion battery
There are many batteries that exist in the world today, and while they all share one main goal, which is to provide power to electrical and electronic devices, they differ in many different characteristics.
Characteristics such as;
- Chemical composition
- Nominal voltage
- Current capacity
- Shape
- Size
- Energy Density
- Specific Energy density
The main characteristic here that plays a major part in determining many of the other factors (such as voltage, current capacity, energy density, etc), is the Chemical Composition.
Batteries produce electrical power from chemical reactions that occur inside the battery. There are a range of chemicals that are used in different batteries which include;
- Nickel-Cadmium (Ni-Cd)
- Zinc-Carbon
- Lithium-Ion (Li-Ion)
- Lead-Acid
- Alkaline
The chemical composition we are most concerned about for this article is Lithium-Ion (Li-On).
The battery is constructed using cells where lithium-ions move from the negative electrode through an electrolyte towards the positive electrode.
Lithium-Ion battery nominal voltage
To better understand at what voltage a Lithium-Ion battery is dead, it will first help to understand the voltage at which it is operational.
The voltage of the battery is one of the most important characteristics when selecting a battery for a particular application.
All electrical and electronic devices have a specific voltage rating that they require to operate efficiently and effectively.
So, you will have to select a battery with the exact voltage (or a bit higher), to satisfy the needs of that device.
The voltage of a battery refers to the amount of electrical potential it is able to hold, and is given in the standard international unit of Voltage (V).
All batteries have a theoretical voltage, however, the actual voltage (nominal voltage) produced will be lower.
This is due to polarisation and resistance losses, and is largely dependent on the current drawn by the load and the internal impedance of the battery.
The maximum voltage that a lithium-ion battery is capable of producing is 4.2V, however this will soon drop to its nominal voltage of 3.7V.
Different types of Lithium-Ion battery
Lithium-Ion batteries come in a variety of shapes and sizes to suit the needs of many different applications, from power tools to RC planes.
Below are the different shapes available for lithium-ion batteries;
- Small cylindrical (single cell with, solid body, with no terminals)
- Large cylindrical (single cell,solid body, with threaded terminals)
- Flat or pouch (soft, flat body)
- Rigid plastic case (large threaded terminals)
But, do the different variety of shapes of lithium-ion batteries share the same voltage?
Yes, while they vary in size, the batteries share the same nominal voltage of 3.7V.
What about devices that require larger voltages, and use lithium-ion batteries? To generate a larger voltage, lithium-ion batteries can be connected in series.
Note, this process is a bit more complicated than connecting other batteries in series, as the impedances of lithium-ion batteries need to be matched.
So, two lithium-ion batteries connected in series (with their impedances matched of course), will now have a nominal voltage of 7.4V.
Adding more batteries will consequently increase the voltage by 3.7V.
Lithium-Ion batteries are available in packs with these higher voltages.
Voltage at which a Lithium-Ion battery is dead
There are a couple of voltages that we need to be aware of when using a lithium-ion battery (or any other battery for that matter).
The first being the nominal voltage, which we now know is 3.7V for lithium-ion batteries.
Another voltage that is of utmost importance is the voltage at which the battery is considered dead, when it has lost all its charge.
It is essential to know this voltage as the battery will need to be recharged back to its nominal voltage to be able to effectively power electronics.
So, what is the voltage at which a lithium-ion battery is considered dead?
The voltage at which a lithium-ion battery is dead is around 3.4V.
If the battery is still connected and continues to discharge past 3.4V, a cutoff circuitry kicks in around 3V and disconnects the battery for protection purposes.
What can affect how fast a lithium-ion battery goes dead?
There are a couple of factors that can affect how fast the lithium-ion battery goes dead, with the two major factors being;
- Load
- Temperature
Load
The first obvious factor is the load that is placed on the battery. A great analogy for this is to imagine you are carrying a backpack (which represents the load), and your energy levels represent the battery.
If you have a lot of items in the backpack, the weight is going to be larger. This means you have to generate more power to carry the load, which is going to cause you to tire faster (lose all your energy).
However, if you only had a few items in the backpack (which meant the weight is far less), you would need to generate less power to carry it. This means you would be able to travel further.
This concept is similar for batteries. If a greater load is placed on the battery (such as powering a motor), the battery is going to have to generate more power causing it to lose charge faster and go dead.
But, if the battery is connected to a device such as an LED (which consumes far less power than a motor), the battery will last much longer.
Temperature
The next major factor that influences the performance of a battery is temperature.
Lithium-Ion batteries have a range of ideal temperatures at which they can be charged and discharged at.
The ideal temperature to charge a lithium-ion battery is 32°F (0°C) to 113°F (45°C) and the ideal discharge temperature is –4°F (-20°C) to 140°F (60°C).
However it is not recommended to charge or discharge the lithium-ion batteries at the extreme temperatures (either real cold or hot).
Higher temperatures can have a temporary advantage of greater performance and increased storage capacity, however, the long term side effect is a decreased life cycle.
Every battery has an internal resistance and when they are subject to drastically lower temperatures, the internal resistance increases.
This means that the battery has to do more work to overcome this increase in resistance causing it to lose power and go dead faster.
What happens when a Lithium-Ion battery is dead
There are two things not to do with a Lithium-Ion battery when it comes to voltage;
- Do not charge them past their maximum safe voltage of 4.2V
- Do not discharge them below the minimum safe voltage of 3V.
Lucky for you and me, we do not have to worry about constantly monitoring the battery to see if the voltage goes past these two limits.
When it comes to charging, lithium-ion batteries require a special charger to ensure that the maximum voltage is not exceeded.
This means lithium-ion battery chargers do not have trickle charging (which is a common technique used to charge a battery when it has reached full charge).
Once the lithium-ion battery has reached full capacity, the battery charger stops charging the battery.
For discharging, lithium-ion batteries include a similar protection circuit that is built on the cell (usually at the the top of the battery covered in tape).
This protection circuit will monitor and disconnect the battery once it has gone dead to protect it from damage. .
Can a lithium-ion battery become dead if it is not used?
Yes, a lithium-ion battery can go dead if it is not used (even though it is not supplying a load).
All batteries have something that is known as shelf life.
The shelf life of a battery tells us the time a battery can hold its charge when it is not being used. After that time, the battery will start to lose charge and need to be recharged (if it is a rechargeable battery).
Lithium-Ion batteries have a self-discharge rate of 5% per month at room temperature.
Irreversible capacity loss occurs if the battery is unused for longer than 12 months.
If the battery is at a voltage of 1.5V or lower, do not try recharging it. Over long periods of time a build of copper shunts can result within the battery which can cause shorts, leading to excessive heating which could result in the worst case scenario of an explosion.
How to check if a Lithium-Ion battery is dead
The easiest way to check the voltage of a lithium-ion battery to see if it is dead is to use a Multimeter.
A multimeter is an electronic measuring instrument that has a range of functions which include measuring voltage, current, resistance, continuity, diode test, frequency, etc.
The number of electrical quantities it is capable of measuring solely depends on the complexity of the multimeter.
However, all standard multimeters will measure the three main quantities which are voltage, current and resistance.
To measure the voltage of a lithium-ion battery, follow the steps below;
- Set the multimeter to voltage mode (ensure the voltage of the battery you are measuring is within the range of the multimeters capability)
- Connect the positive (red) lead of the multimeter to the positive terminal of the battery
- Connect the negative (black) lead of the multimeter to the negative terminal of the battery
- Note the voltage that the multimeter displays
Should you continue to use a Lithium-Ion battery when it is almost dead? 00
If you measure the voltage of a lithium-ion and it happens to be nearing its dead voltage of 3.4V, should you continue to use it?
No, the best option here is to recharge the battery.
Using a battery when it is almost dead can drastically reduce its lifespan.
