On top of charging mobiles, tablets and other gadgets, did you know that you can use a power bank to charge a laptop?
If your laptop is going to run out of battery and you do not have its charger at hand you can resort to a power bank to continue working or you can also use it as an external battery if the battery of your laptop is broken and you always need to have an outlet nearby.
A power bank can perform the same function as a laptop charger but not just any model will do, it must meet a number of requirements to work as a substitute for the charger:
- Connector: include a cable with a connector compatible with the laptop’s charging port.
- Voltage (V): same working voltage.
- Power (W): same or greater power supplied.
In this Guide we will learn how to identify a laptop power bank taking into account the above requirements and, as always, we will recommend the best models available on Amazon.
- 1 Features of a laptop charger
- 2 Using a power bank as a laptop charger
- 3 How much power does a power bank need to charge a laptop?
- 4 How many hours would I be able to use a laptop with a power bank?
- 5 Quick guide and real use cases 📝
- 6 Best power banks for laptops (May 2022) 🚩
Features of a laptop charger
First of all, we need to know the specifications of our laptop charger in order to find a power bank that meets the same requirements.
In the following image we can see the specifications of a laptop charger:
We must check the output parameters (Output):
- Voltage: 19.5V
- Current/Amperage: 4.62A
This means that this charger works at a voltage of 19.5V (volts) and supplies a maximum current of 4.26A (amps).
This charger does not indicate the maximum power that it can supply but we can easily obtain it by multiplying the voltage by the current:
- Power: 19.5V x 4.62A = 90W
Using a power bank as a laptop charger
Next, we need to find a power bank that replaces our charger and meets the following characteristics:
A laptop can be powered through a power bank in 3 different ways, depending on the OUTPUT port it has:
There are 3 types of laptop power banks on the market:
Output port voltage (V) ❗
If we choose to buy a power bank with DC or USB-C PD output it is very important to check that the output port of the power bank has the same voltage* as your laptop charger, otherwise you could irreversibly damage your computer.
This output voltage will always be indicated in the power bank specifications as “DC Output” or “USB-C Output”.
On the other hand, we can also find models that may have one or more DC output ports with a fixed voltage or a single multi-voltage DC port, whose voltage can be selected (by pressing the “Power” button) to the charging voltage of our laptop.
Obviously, if we were to use a power bank with AC output it is not necessary to check the voltage because we would continue to power the laptop with its own charger (which is already in charge of transforming the 220V voltage to the computer charging voltage).
Power supplied (W)
Finally, we must take into account the maximum power that can be supplied by the output port of the power bank:
If the charger of our laptop is 65W then it is advisable to use a power bank that is capable of providing the same or higher power than the charger, because, otherwise, the computer would not even start up as it needs the maximum power during its start-up (and subsequent use) at the same time as it recharges its battery.
However, in the following section we will look at some situations in which it is possible to use a lower power model:
How much power does a power bank need to charge a laptop?
Depending on the laptop model, your charger will be designed to supply a maximum amount of power, i. e: 45, 65, 90 or 130W.
We may not find a power bank that provides the same or a higher amount power than our portable charger either by specifications or budget. In this situation, we can also buy a lower powered power bank.
Let’s say we are working in a coffee shop with our Lenovo Z50-70 laptop (its charger is 65W) and we run out of battery.
We could use a 65W power bank or resort to a lower power one, for example, 45W, to be used under certain conditions:
How many hours would I be able to use a laptop with a power bank?
Let’s suppose we are interested in buying a power bank to charge our laptop and we want to know how much extra time we could continue working with the power bank connected.
First of all, it is important to consider the following questions for the right choice of power bank:
- To get an idea of the average power consumption of your laptop, what kind of tasks do you usually use your laptop for? For example: surfing the web, office, gaming, watching Netflix..
- For your chosen tasks, how many hours does your laptop last with a 100% charged battery?
- What is your budget?
- What type of laptop power bank do you want to use, with DC, AC or USB-C Power Delivery port?
Now, we are going to see an example using a laptop with the following features:
- Brand: Acer
- Model: Aspire E5-551-T2HE
- Charger: 19V/3.42A (65 W)
- Charging voltage: 19V
- Battery capacity: 45Wh
- Charging port: DC jack 5.5 x 1.7 mm
- Regular Usage Tasks: office tasks and web surfing.
- Battery life 100%: 3.5h
Although our Acer laptop has a DC charging port, we decided to purchase a power bank with USB-C PD port along with a USB-C PD to DC adapter cable:
- Brand: Litionite
- Model: Vulcan 20000mAh PD 65W
- Battery capacity: 74 Wh (20000 mAh/3.7V)
- USB-C PD port: 5V-20V (65W max)
- PD power: 65 W
- Charging voltages: 5V- 20V* (check here)
- USB-C PD to DC jack 5.5×2.1 20V cable
- Adapter: DC jack 5,5×2,1 to DC jack 5,5×1,7
Next, let’s calculate the approximate time we can use our Acer Aspire E5 laptop with the Litionite Vulcan power bank:
Calculating the average power consumption of our laptop
If we don’t have enough knowledge or the necessary tools to measure exactly the average consumption of our computer, we can make an estimate taking into account:
- The energy stored in the laptop battery.
- The estimated duration time for the tasks we usually perform with our laptop.
The energy stored in the notebook battery – measured in watt-hours (Wh) – can be found in the specifications of the battery itself.
This data may be displayed directly or, if not, it must be calculated by multiplying the voltage (V) by the capacity (mAh) of the battery.
For example, in the battery specifications of the left image the energy stored in the battery would be 49 Wh while the image on the right would be 73.26 Wh (11.1V x 6600mAh / 1000).
Once we know the energy stored in the laptop battery we must divide by the time (expressed in hours) that the laptop lasts when its battery is fully charged (100%):
In our example, the Acer Aspire E5 laptop battery is 45 Wh and we have about 3.5 hours to use it for everyday tasks before its battery is completely drained.
Therefore, our laptop consumes an average of 12.9 watts (W):
Acer Power Consumption = 45 Wh / 3.5 h = 12.9 W (watts)
Of course, the consumption of our laptop and, therefore, the battery life will vary depending on the tasks we are performing at that moment.
Surfing the web is not the same as playing a game that demands maximum CPU and GPU performance, for example.
Calculating the useful energy of a power bank for laptop charging
Once we have an estimate of the consumption of our laptop we will calculate the number of hours we could continue to use it with a power bank.
At first, one may think that one should simply apply the following formula:
Laptop usage time (h) = Power bank Energy (Wh) / Avg. Laptop Power Consumption (W) ERROR!
The above formula is not valid, as we must take into account the energy efficiency of the power bank and the laptop during the charging process as well as other factors that we will see below.
In conclusion, the energy supplied at the USB output port of a power bank will be different from the energy stored in its battery and can be calculated by the following formula:
Power bank Useful Energy = Stored Energy x Energy Efficiency
Therefore, following our example, the useful energy that the Litionite Vulcan power bank can supply to a device would be:
Litionite Useful Energy = (74 Wh x 85) / 100 = 62.9 Wh
Once we know the power consumption of our Acer Aspire E5 and the useful energy of the Litionite Vulcan power bank, we need to know the energy required to fully recharge the laptop battery.
Remember that a laptop with DC input can be powered through a power bank in three different ways, depending on the output port (OUTPUT) that the power bank has:
- Power bank with DC port
- Power bank with AC port
- Power bank with USB-C PD port
Next, we are going to analyze the different “particularities” that our power bank may have depending on the output port used:
Calculating the usage time of a laptop with a power bank
At this point, there are 3 different cases in the use of the useful energy of a power bank.
We will formulate each case to obtain a general formula for the usage time of a laptop with a power bank and then apply it to our example of the Acer Aspire E5 laptop and the Litionite Vulcan power bank.
In addition, we will compare the results obtained in each formula with the data we actually obtained in this example.
Finally, remember that this is not an exact calculation, we are talking about an estimate to help us know the approximate time of use before buying the power bank.
Conclusions and general formula
In the first 2 cases described, we saw that the theoretical usage time was similar while the actual usage time suffered small variations.
This is because we are working with real efficiencies, both in the laptop and in the power bank and, logically, they must differ from the theoretical efficiencies (85%) that we establish as a reference for the estimated calculation when we do not know the real efficiencies.
The most common is not knowing both the real efficiency of our computer and that of the power bank we are going to use to recharge it.
We also explained in Case 3 that it is not possible to use a general formula to predict the usage time because each laptop behaves differently during its battery recharge. However, the actual results obtained are similar to the first 2 cases.
Remember that the objective is to have an idea of the time of use of our laptop before buying a power bank, for this reason, we believe that the formula of case 1 is the best option for a quick estimate:
Quick guide and real use cases 📝
In this section we will try to summarize the essential content of this guide by linking to the sections you need to consult to buy a laptop power bank.
1. Choosing the type of laptop power bank
Depending on the type of output port of the power bank we will have to make several checks:
2. Laptop usage time with a power bank
Once you have chosen the power bank, we will theoretically calculate the estimated time you could use your laptop for a certain regular activity (watching Netflix, Youtube, office tasks, surfing the Internet, playing online games…) depending on the charging method: laptop battery removed, laptop turned off or using the laptop while charging:
3. Real tests of charging a laptop with a power bank
Next, we are going to see the theoretical and real results obtained by charging some laptops with a power bank:
Best power banks for laptops (May 2022) 🚩
Once you are familiar with the features of a laptop power bank, we present the best models available on the market taking into account the different types of output ports: DC, AC and USB-C PD.
Notice: Remember that if your laptop has a DC charging port and you choose to buy a power bank with USB-C PD port you need to use a USB-C PD to DC adapter.