There are many ways to charge your phone. You can use a wall adapter, wireless charger, or even a power bank to recharge its battery when needed. However, sometimes you don’t have access to any of these options and are left with just your laptop. Fortunately, your laptop’s USB ports can transfer power to other devices, including your phone. While it might not seem like the best way to recharge your phone’s battery, charging via your laptop’s USB ports is perfectly safe. In fact, some USB-C ports are capable of delivering up to 240 W.
USB, which stands for Universal Serial Bus, generally comes in two forms: Type-A, the rectangular connector, or Type-C, an oval connector. Older USB ports only carry 5V; newer ones, which support Power Delivery (PD), can go much higher, up to 48V.
To keep things safe, power doesn’t automatically start flowing to your phone when you plug it in. Instead, both devices negotiate a safe power consumption, and only this is supplied to your phone. All the negotiation is handled by your phone’s Power Management Integrated Circuit (PMIC). This is the technology that ensures your phone charges efficiently and safely when you connect your phone to a laptop or high-power wall adapter.
However, there is one big caveat to charging your phone from a laptop. Laptop USB ports are typically designed to provide a limited amount of power, meaning your phone will charge slowly and may take hours to fully charge. Additionally, the laws of physics mean that some energy will be used and dispersed when moving from one device to another.
How fast will a laptop charge your phone?
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When you charge your phone using your laptop, the charging speed largely depends on the capabilities of the USB port. USB Type-A ports with USB 2.0 support will give you 2.5W. If you have a USB 3.0 or next-generation Type-A port, that amount rises to 4.5W. Although some dedicated USB Type-A charging ports can reach up to 7.5W for charging, these are relatively rare on laptops.
USB-C ports, on the other hand, can be more powerful in terms of power delivery. Still, most Type-C ports you’ll find on laptops are limited to 15W. Although the USB-PD specification allows Type-C ports to offer up to 240W of power, laptop manufacturers have yet to use it to power or charge other devices. The reason for this is probably that the power consumption would put too much strain on the laptop’s built-in battery. However, some laptops support USB-PD when charging. But that’s strictly for power consumption.
Dell mentions that all USB-C ports on its laptops, including those with Thunderbolt 3 and Thunderbolt 4 capabilities, can deliver up to 15W. Framework also offers 15W or less output power for all USB-C ports on its laptops.
Laptops may limit USB output power when running on battery power for power saving purposes. Therefore, even if a laptop has a 15W capable USB port, it may not deliver as much power when running on battery power. Additionally, if there are multiple USB ports on a laptop, the order in which they are used may matter. Chances are that the first USB port you connect to will get the most power available and the output will decrease for the others.
