Plug it into a wall outlet or USB port, just like you charge your phone

A portable charger charges the same way your phone does: you connect a cable to the charger's input port and plug the other end into a power source. Most portable chargers use a USB-C or micro-USB input port. The cable comes with the charger, or you can use any compatible cable you already own. Plug the wall end into an outlet, a power strip, or a USB power adapter (the brick that came with your phone or laptop). The charger will draw power until its battery is full, which usually takes two to six hours depending on the charger's size and the power source you use.

Some newer portable chargers support fast charging, which means they'll fill up faster if you use a higher-wattage power adapter — typically 20 watts or more. Check the charger's manual or the label on the back to see what wattage it supports. Using a lower-wattage adapter will still work, but it will charge more slowly.

Key Takeaways

  • Portable chargers charge through a USB-C or micro-USB input port using any compatible cable and a standard wall outlet or USB power adapter.
  • Charging time ranges from two to six hours depending on the charger's capacity and the wattage of the power adapter you use.
  • A higher-wattage adapter (20 watts or more) will charge a portable charger faster if it supports fast charging.
  • Most portable chargers have an LED indicator or button that shows how full the battery is while charging.
  • You can charge a portable charger while it's charging your phone, though this slows down both processes.

Check the LED indicator or press the power button to see how full it is

While your portable charger is plugged in, look for an LED light or a row of small lights on the device. These lights show you how much the battery has filled up — usually one light means 25 percent, two lights mean 50 percent, and so on. Some chargers use a single light that changes color: blue or green means it's charging, and it may turn off or change color when the battery is full.

On some models, you need to press the power button to see the charge level. Press it once and the lights will flash to show you the current percentage. This is useful if you want to check progress without leaving the charger plugged in the whole time.

Use the right cable and power adapter for faster charging

The cable that came with your portable charger is designed for that specific input port. If you've lost it, buy a replacement cable that matches your charger's input port — USB-C, micro-USB, or Lightning (on some Apple-compatible chargers). Using the wrong cable type won't damage anything, but it won't fit.

The power adapter matters more than most people realize. A 5-watt adapter (the kind that came with older phones) will charge your portable charger, but slowly. A 20-watt or 30-watt adapter will do the job in roughly half the time, as long as your charger supports fast charging. Check the manual or the specifications printed on the back of the charger to see the maximum wattage it accepts. If you use an adapter with higher wattage than the charger supports, the charger will straightforward charge at its maximum safe speed — it won't overheat or break.

Charge it at home before you leave, not in your bag

Charge your portable charger when you're at home or at a desk, not while it's sitting in your backpack or bag. Portable chargers generate a small amount of heat while charging, and that heat needs somewhere to go. If the charger is wrapped in fabric or surrounded by other items, the heat can build up and slow down charging or, in rare cases, damage the battery over time.

Make it a habit to charge your portable charger the night before you plan to use it, or whenever you get home after using it. This way it's always ready and you're not scrambling to charge it in your car or at the airport.

You can charge your phone and the portable charger at the same time

If you're in a hurry, you can plug your phone into the portable charger while the charger itself is plugged into a wall outlet. The charger will send power to your phone while also drawing power from the wall. However, this slows down both processes — your phone charges more slowly than it would if the charger wasn't also being charged, and the charger fills up more slowly than it would if it wasn't powering your phone.

This setup is fine for an hour or two in an emergency, but it's not ideal for overnight charging. If you have time, charge the portable charger first until it's full, then unplug it from the wall and use it to charge your phone.

Avoid leaving it plugged in for days or storing it completely empty

Once your portable charger is full, unplug it. Leaving it plugged in for days doesn't damage the battery when ready, but it does stress it slightly over time. Most modern chargers have built-in protection that stops charging once the battery is full, but unplugging after a few hours is still the better habit.

On the other end, try not to let your portable charger sit completely empty for months. If you're not using it, charge it to about 50 percent and store it in a cool, dry place. A battery that sits at zero charge for a long time can lose its ability to hold a charge. If you do forget about it and it drains completely, plug it in and let it charge normally — it will usually recover, though it may not hold quite as much power as before.

Troubleshoot if your charger won't charge or charges very slowly

If your portable charger isn't charging at all, try a different cable first. The cable is the most common failure point, and a frayed or damaged cable won't conduct power even if it looks fine. If a different cable works, replace the original one.

If the charger still won't charge with a new cable, try a different power outlet or adapter. Some outlets are controlled by wall switches and may be turned off. If you're using a USB port on a computer or a low-power adapter, switch to a wall outlet with a standard power adapter instead.

If your charger charges very slowly, you're probably using a low-wattage adapter. Switch to a 20-watt or higher adapter if your charger supports it. Also check that the charger isn't hot to the touch — if it is, unplug it and let it cool down for 30 minutes before trying again. Heat buildup can cause the charger to slow down its charging speed as a safety measure.

Frequently Asked Questions

How long does it take to fully charge a portable charger?

Most portable chargers take two to six hours to charge completely, depending on their capacity and the wattage of your power adapter. A small 5,000 mAh charger with a 5-watt adapter might take three hours, while a large 20,000 mAh charger with a 30-watt adapter could take four to six hours. Check your charger's manual for the exact time.

Can I use any USB cable to charge my portable charger?

Yes, as long as the cable matches your charger's input port. If your charger has a USB-C port, use a USB-C cable. If it has micro-USB, use a micro-USB cable. The cable doesn't have to be the original one that came with the charger, but it does have to be the right type.

Is it bad to leave a portable charger plugged in overnight?

It's not dangerous, but it's not ideal for long-term battery health. Modern chargers stop charging once the battery is full, but unplugging after a few hours is still better. If you regularly leave it plugged in for 12+ hours, the battery may lose some capacity over months or years.

Why is my portable charger charging so slowly?

You're probably using a low-wattage power adapter. Try plugging into a wall outlet with a 20-watt or higher adapter instead of a computer USB port or a 5-watt phone charger. If the charger feels hot, unplug it and let it cool down — heat causes the charger to slow itself down for safety.

Can I charge my portable charger in my car?

Yes, if your car has a USB port or a 12-volt outlet with an adapter. Car charging is slower than wall charging because car USB ports usually provide only 5 watts of power. If you need faster charging, use a wall outlet when you're home or at a location with one available.