How to Charge One Phone Using Another Phone's Battery

You can charge another phone with your own phone, but only if your phone has a feature called reverse wireless charging or if you carry a portable battery pack

Most phones cannot transfer battery power to another phone through a cable or wireless connection. The hardware and software straightforward are not built for it. However, some newer phones — mainly Samsung Galaxy flagships and a few others — have reverse wireless charging, which lets you place another phone on the back of your phone to transfer power wirelessly. If your phone does not have this feature, your only practical option is to carry a portable battery pack (also called a power bank), which stores charge separately and can power multiple devices.

The method you use depends on what phone you own, what phone needs charging, and whether you have the right cables or accessories on hand. Neither method drains your phone when ready — reverse wireless charging is slow, and a battery pack is designed for this job — but both require planning ahead.

Key Takeaways

Reverse wireless charging works only on certain phones, mainly Samsung Galaxy S21 and newer models, and transfers power slowly (around 4.5 watts).
A portable battery pack is the most reliable way to charge another phone and works with any phone that accepts USB power.
Reverse wireless charging drains your phone's battery faster than normal use, so use it only when both phones are plugged into power or when you can afford to lose significant charge.
Battery packs come in different sizes and capacities; a 10,000 mAh pack can fully charge most phones once or twice.
Both methods require the receiving phone to support wireless charging (for reverse charging) or to have a compatible charging port (for battery packs).

How reverse wireless charging works

If your phone has reverse wireless charging, you can place another phone face-down on the back of your phone to transfer power. The receiving phone must also support wireless charging — it cannot be an older model or a phone without a wireless charging coil. Samsung Galaxy S21, S22, S23, and S24 models have this feature, as do some OnePlus and Xiaomi phones, but the feature is not standard across all brands.

To use reverse wireless charging, turn on the feature in your phone's settings (usually under Battery or Advanced Features), then place the other phone flat against the back of your phone. The transfer is slow — typically around 4.5 watts — so a full charge takes several hours. Your own phone's battery will drop noticeably during this time. For this reason, reverse wireless charging works best when both phones are plugged into power, or when you are in a situation where you can afford to lose 20 to 40 percent of your battery to help someone else.

The feature is convenient in emergencies — if a friend's phone dies and you both need to stay reachable — but it is not a substitute for a proper charger or battery pack. The slow speed and battery drain make it impractical for everyday use.

Choosing and using a portable battery pack

A portable battery pack is a separate device that stores electrical charge and plugs into your phone (or another phone) via USB cable. Unlike reverse wireless charging, a battery pack does not drain your own phone's battery. It is the most reliable way to charge another phone, and it works with any phone that has a USB port or accepts USB power.

Battery packs come in different sizes, measured in milliamp-hours (mAh). A 10,000 mAh pack can fully charge most modern phones once, or charge a phone twice if the phone's battery is smaller. A 20,000 mAh pack can charge most phones twice or a larger phone once. Smaller packs (5,000 mAh) fit in a pocket but charge a phone only partially. Choose based on how often you need backup power and how much space you want to carry.

To use a battery pack, connect it to the phone that needs charging with the appropriate cable — USB-C, Lightning, or Micro-USB, depending on the phone. The pack will begin transferring power automatically. Most packs have a button you can press to check how much charge remains, shown by LED lights or a small screen. When the pack itself runs low, plug it into a wall outlet or computer to recharge it.

What to look for in a battery pack

The most important feature is capacity — how much total charge the pack holds. A 10,000 mAh pack is a good middle ground for most people: small enough to carry daily, large enough to charge a phone fully. If you travel frequently or have a large phone, consider 20,000 mAh or higher. If you only need occasional backup, 5,000 mAh is lighter and cheaper.

The second consideration is charging speed, measured in watts. Most battery packs charge at 10 to 20 watts, which is slower than a wall charger but acceptable for backup use. Some newer packs support 30 watts or higher, which charges faster but costs more. Check whether the pack includes the cable you need — some include USB-C, others require you to buy a cable separately.

Finally, check whether the pack has multiple ports. A pack with two USB ports can charge two phones at once, though the speed will be slower for each. A pack with one USB-C port and one USB-A port gives you flexibility to charge different phone types simultaneously. This matters if you regularly need to charge multiple devices.

When reverse wireless charging drains your phone too much

Reverse wireless charging is convenient but expensive in terms of battery life. Your phone will lose 20 to 40 percent of its charge to transfer power to another phone, depending on how long the transfer takes. If your own phone is already below 50 percent battery, using reverse wireless charging puts you at risk of your phone dying before you can reach a charger.

For this reason, only use reverse wireless charging when your phone is plugged into power, or when you are certain you will not need your phone's full battery for the rest of the day. If you are traveling, in a situation where you cannot reach a charger, or if your phone is your only communication device, use a battery pack instead. A battery pack protects your own phone's battery while still helping someone else.

Cables and ports: making sure devices are compatible

If you are using a battery pack, the cable matters. Most modern phones use USB-C, but some older iPhones use Lightning, and some older Android phones use Micro-USB. A battery pack with a USB-C port will charge any USB-C phone. If you need to charge multiple phone types, buy a pack with multiple ports or carry multiple cables.

For reverse wireless charging, both phones must have wireless charging coils built in. You cannot use reverse wireless charging to charge a phone that does not support wireless charging, no matter what phone you own. Check your phone's specifications or manual to confirm it has wireless charging before relying on this method.

How fast does charging actually happen

Reverse wireless charging is the slowest option. At 4.5 watts, it takes 3 to 5 hours to fully charge a typical phone. A battery pack is faster — usually 1 to 3 hours depending on the pack's wattage and the phone's battery size. A wall charger is fastest, typically 30 minutes to 2 hours for a full charge.

If you need a phone charged quickly, a battery pack is more practical than reverse wireless charging. If you have time and both phones are plugged into power, reverse wireless charging works but is not efficient. In an emergency where you need a phone usable within an hour, a battery pack is your best bet.

Frequently Asked Questions

Can I charge an iPhone with an Android phone?

Only if both phones support wireless charging and your Android phone has reverse wireless charging. iPhones have wireless charging, but not all Android phones do. If your Android phone does not have reverse wireless charging, you cannot transfer power to an iPhone wirelessly. A battery pack works with both iPhones and Android phones regardless of brand.

Does reverse wireless charging damage either phone's battery?

No, but it does drain the sending phone's battery faster than normal use. Wireless charging generates a small amount of heat, which is normal. If you use reverse wireless charging frequently, your phone's battery may degrade slightly over time, just as it would with any repeated charging cycle. For occasional emergency use, the impact is minimal.

What size battery pack do I actually need?

A 10,000 mAh pack is sufficient for most people and fits in a bag or large pocket. If you travel for multiple days without access to a charger, or if you have a large phone, consider 20,000 mAh. If you only charge your phone once a week as backup, 5,000 mAh is enough and lighter to carry.

Can I charge a phone and use reverse wireless charging at the same time?

Yes. If your phone is plugged into a wall charger, you can use reverse wireless charging to charge another phone without draining your own battery. This is the safest way to use the feature because your phone stays at full charge while transferring power to the other device.

Do battery packs work with all phones?

Battery packs work with any phone that has a USB port or accepts USB power. You need the correct cable for your phone's charging port — USB-C, Lightning, or Micro-USB. Most modern phones use USB-C, but check your phone's port before buying a pack to make sure the cable matches.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.