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What is pass-through charging in power banks?

One of the technological features of power banks is pass-through charging. We list it among the rest of the key features of our individual product reviews from our review section. For example, here it is listed on the review of the iHome Ultra Boost 10000mAh:

pass through charging

Although the naming is pretty intuitive, we wanted to dive a bit deeper and shed some more light on this topic.

What is pass-through charging?

Pass-through charging is, in the simplest terms, a technology built into power banks that allows a device to be connected and recharged while the power bank is plugged into a wall socket and charging itself. This technology makes use of a series of power regulating circuits that match the amount of energy needed by a connected device to the amps being drawn out from the wall outlet.

If this is done correctly, pass-through will send power straight from the wall socket to the output device connected to the power bank. However, it will charge either at a slower or regular rate, depending on the load balance performance of the power bank.

How does pass-through charging actually work?

First of all, you should know that pass-through charging is not supported by all power banks. If you own one that doesn’t have it and you plug the power bank into a wall outlet then the outputs will turn off and will remain in that state until manual intervention. If that doesn’t happen, then it’s more likely there will be damage to the power bank and the battery. It’s actually pretty unsafe to do this since it would deliver an outward current that creates energy, which in turn, generates heat, causing the battery to degrade faster.

Otherwise, if it supports simultaneous charge and recharge, then what will happen is both the connected device and power bank will become fully replenished. However, the amount of energy going into the power bank is limited, and only some of it will go into the connected device and some to the unit. So it will take a long time to fully recharge both devices.

It’s important to note that a battery can’t charge or discharge at the exact same time. It’s impossible for it to do something like this because the current only moves in one direction at a time. This means the power bank is not actually being charged while replenishing a connected device simultaneously.

What actually happens is quite similar to connecting a phone to a wall charger. The very first thing that happens when you do this is that the phone will switch to be being powered by the charger. Otherwise, it wouldn’t be able to replenish the battery. What happens to the battery solely depends on how much energy is available from the charger and the power needed by the phone.

When a phone is connected to a power bank, which is plugged into a wall outlet, then the power will be sent straight to the phone. This will cause it to take the full output from the power bank. If the charge input of the power bank is larger than its output, then it will replenish the battery at the same time. If it’s not, then it will discharge the battery to increase the output power.

However, if the battery goes down to 0%, then the output will shut off, which will allow the power bank battery to take full power from the wall socket. So, if you have a device connected while this happens, it may not get charged until the output is turned on again.

Can pass-through charging affect battery life?

Pass-through charging may affect the battery life of your power bank. If it effectively uses internal circuitry to match both the input and output levels, then there may not be much effect on the charge capacity over time.  Power banks can also lose power capacity from recharging and discharging their batteries.

Battery degradation can also be influenced by build quality. Companies with a strong reputation that work with pass-through charging often develop their power banks out of rigid components, which helps to keep the battery from degrading.

To prevent any damages to your connected device or power bank, you should do two things. Firstly, you should ensure that your power bank has the right circuitry built-in to support pass-through charging. Secondly, it’s best to only use the unit for a short amount of time if you plan on using this feature. It should be used in emergencies instead. This will enable you to keep it from building up heat while reducing the risk of battery damage