Does Charging Power Bank with Power Bank Work? Here to Tell

You rely on a power bank when your phone battery is running low, but what happens when your power bank itself runs out? If you're carrying, or can borrow a second one, you'd normally just use that. Still, many people wonder about charging power bank with power bank.

Maybe it's to top up a smaller, more portable unit to take with you, or because one has the right port for a specific device. The idea seems clever, but the reality is less straightforward. Before you plug one into the other, it's worth understanding how power banks work, the risks involved, and what smarter options you have.

How Do Power Banks Work?

Before we can answer the question, "Can I charge a power bank with another power bank?" let's first see how a portable power bank works. At their core, power banks are just rechargeable batteries paired with smart electronics that control how energy flows in and out.

Here's what's happening inside:

Battery cells

Most power banks use lithium-ion cells that store energy at around 3.6-3.8 volts (V). 3.7V is the most common. The capacity you see on the box, like 10,000 mAh or 20,000 mAh, is measured at this internal cell level.

Power control circuit

This is the "brain" of the power bank. It manages charging, discharging, and safety features. It makes sure the cells don't overheat, overcharge, or discharge too quickly.

Voltage conversion

When you plug in and charge a device, the power bank boosts its 3.6-3.8V cell output up to a standard USB level your phone or laptop expects. That's usually 5V, or higher voltages if both sides support USB-C Power Delivery (PD).

When you recharge the power bank itself, the incoming power from a wall adapter is stepped down to the right level to safely fill the cells.

Smart negotiation

On USB-C, the cable and devices "talk" to each other over control pins. They decide who provides power (Source), who receives it (Sink), and at what voltage and current. Some ports are dual-role, meaning they can act as either input or output depending on what's connected. You'll often see them labelled as "IN/OUT"

One more detail: no energy transfer is perfect. During every conversion, some power is lost as heat. Well-designed power banks typically run at 80-90% efficiency. That's why a 10,000 mAh bank won't fully deliver 10,000 mAh to your phone.

Can You Charge a Power Bank with Another Power Bank?

The short answer: sometimes yes, but it's usually not worth doing.

Technically, the key to the connection lies in the charging ports:

• The familiar USB-A ports you see on most power banks are output only. They can't receive a charge.
• Many power banks (especially older or cheaper models) have a micro-USB or USB-C port that is only for charging the power bank itself.
• Modern power banks use USB-C with "dual-role" or "bidirectional" design. That means the same port can act as input or output depending on what's plugged in.

So, what happens if you plug two power banks together?

One charges the other

If you connect a USB-A output from one power bank to the input-only micro-USB or USB-C port on another, energy will flow. The first bank discharges, and the second begins to recharge. You can tell from the blinking LEDs on both.

Over USB-C, it can be more dynamic. Dual-role ports use control CC pins and the USB Power Delivery protocol to decide roles. Typically, the power bank with more charge, like 50%, becomes the power Source. It will start topping up the other one with, let's say 20% battery left.

Or nothing happens

If you try connecting two input-only ports, or an output-only port to another port marked "OUT," no current flows.

Even with dual-role USB-C ports, both power banks need to agree on who is Source and who is Sink. If they both try to source power, or both try to receive, or if a role swap isn't supported, the connection fails.

So, yes, a power bank can charge another, but only when the ports line up correctly.

Risks and Drawbacks of Charging One Power Bank with Another

Now, we've established that charging a power bank with another is technically possible if the ports allow it. It's a trick that may help in an emergency, but it's not a smart everyday practice. Here's why:

Inefficiency from double conversion

A power bank's internal cells store energy at about 3.7V. To send that energy out, the electronics boost it up to 5V, 9V, or higher. When you use it to refill another power bank, the receiving end immediately steps that voltage back down to recharge its own cells.

Each step burns off some of the energy as heat. Even well-engineered packs run at about 80-90% efficiency per step. So, when you chain them, the overall efficiency drops sharply. The end result? You waste 20-30% more energy than if you had just used the two banks independently.

More heat, shorter lifespan

Those extra conversions raise temperatures inside both power packs. Heat is the main factor that accelerates wear in lithium-ion batteries, so frequent bank-to-bank charging means faster aging.

Role confusion and failed connections

Not all power banks are built to negotiate cleanly with each other. With dual-role USB-C ports, the two banks sometimes fail to agree on who should send and who should receive power. The result can be no charge at all. Or in some cases, the handshake keeps failing, causing power to cycle on and off.

Added strain without added benefit

Each time you discharge one bank and recharge another, both go through extra cycles. Every cycle counts toward battery wear. Because you also lose energy in the process, you're reducing the lifespan of two devices just to end up with less usable power overall.

Smarter Alternative Ways to Charge Power Banks

Given the drawbacks, chaining battery packs should really be a last resort. Luckily, there are plenty of smarter, more efficient ways to keep your power banks ready for action.

1. Use a proper USB-C PD wall charger

The most reliable way to recharge a power bank is still a wall adapter that matches its input rating. A good USB-C Power Delivery charger negotiates the highest safe voltage and current, so your bank fills quickly and efficiently.

2. Top up from a car's outlet

On the road, a PD car charger connected to the 12V or 24V cigarette lighter socket is the simplest option. It avoids chaining batteries and gives you stable charging while you drive.

3. Hybrid "charger + power bank" options

Some devices are designed to be both a wall charger and a portable pack. Plug them into a wall socket and they act like a normal high-watt charger; unplug and they become a battery pack you can carry.

For example, the Anker Prime Power Bank (9.6K, 65W) is such a 2-in-1 "Fusion" model with 9,600mAh capacity. When you flip out the AC prongs and plug it into the wall, its USB-C ports behave like a 65W charger.

Another one of these power bank with charger hybrids is the Anker 733 Power Bank (GaNPrime PowerCore 65W). Plug it into AC and it acts as a 65W charger; unplug and it's a 10K power bank.

Because these power banks function as chargers, they can also top up another power bank directly.

4. Pass-through charging

Pass-through means a power bank can recharge itself and deliver power to another device at the same time. It's useful if you want to keep everything topped up at a desk or nightstand without swapping cables. Not every model supports it, so check first.

For those that do though, you also have wireless charger with power bank options.

Qi2 certified, the Anker MagGo Power Bank (10K) explicitly lists pass-through charging and has a foldable stand. Snap your MagSafe-enabled iPhone on, plug the bank into a wall adapter, flip out the stand, and it behaves like a Qi2 wireless charging stand. The pack tops itself up, too.

5. Charging bases for power banks

Some of the newest power banks are designed to work with dedicated charging bases. Instead of plugging in a cable, you simply drop the bank onto a dock with pogo-pin connectors, and it begins refueling automatically.

The base itself doubles as a high-speed desktop charger, so you can charge the bank and other devices at the same time. This setup cuts cable clutter and makes recharging heavy-capacity banks far more convenient.

Sounds wonderful? One flagship model that supports this is the Anker Prime Power Bank (26K, 300W). With two USB-C ports rated up to 140W each and an additional USB-A at 22.5W, it can push out a combined 300W. That's enough to fast charge two laptops and your phone simultaneously.

When it's time to recharge, it supports up to 250W dual-port input from USB-C, filling to 80% in around 30 minutes. On the Prime charging base, it still pulls a strong 150W, making drop-and-charge reloading fast and easy.

A slightly smaller but still powerful option is the Anker Prime Power Bank (20K, 220W). This model delivers 140W from either of its two USB-C ports without derating, plus 22.5W from USB-A, for a total of 220W output.

Built with a magnesium-aluminum alloy shell, it offers better heat dissipation and a compact design that's smaller than a soda can. It's easy to carry and comfortable to hold. It's also compatible with the Prime charging base, which recharges it quickly while keeping your desk setup clean.

Conclusion

As you can see, charging power bank with power bank is possible, but it's rarely the smartest choice. The process wastes energy, generates heat, and puts unnecessary strain on both batteries. A better approach is to use proper USB-C PD chargers, car adapters, or modern solutions like hybrid charger-power banks or charging bases. These methods keep your devices powered efficiently without sacrificing battery life. At Anker, you'll find reliable options across all these categories, designed to deliver safe, fast, and practical charging wherever you need it.

FAQs

Is it okay to charge your phone through a power bank while the power bank itself is being charged?

Only if your power bank specifically supports "pass-through charging". Many models don't, since it can shorten battery life or cause extra heat buildup. If your device does support it, charging will usually be slower, and the unit may get warm. Always check your power bank's specifications before trying pass-through charging.

Is it okay to charge a power bank with two chargers?

Usually not. Most power banks are built to accept just one charging input at a time. That said, some high-performance models do support dual input. For instance, the Anker Prime Power Bank (27K, 250W) allows dual USB-C charging up to 170W, and the Anker Prime Power Bank (26K, 300W) supports up to 250W dual input, recharging to 80% in about 35 minutes. Unless your manual confirms this feature, stick with a single charger to avoid damage.

Can you carry two power banks?

Yes, but they must go in your carry-on bag, never in checked luggage. According to airline safety rules, power banks are treated like spare lithium batteries. Those rated up to 100 Wh (about 27,000mAh) are generally fine, and airlines usually allow several. For larger ones between 100 Wh and 160 Wh, you can usually bring only two, and you'll need airline approval. Always double-check your airline's specific policy before flying.

Why are power banks not allowed on flights?

Power banks aren't banned completely, but they're restricted to carry-on bags only. This is because they use lithium-ion batteries, which can overheat and, in rare cases, go into thermal runaway. If a battery incident happens in the cabin, the crew can spot and handle it quickly. In the cargo hold, that's much harder, which is why airlines require you to keep power banks with you during the flight.