We generally think of charging cables as inert unless they are connected to a charger at one end and a device that is in need of charging on the other.

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That's not the case when it comes to Apple devices.

No, Apple cables are so smart that they draw a small amount of power even when there's no device connected to the other end. 

One culprit is Lightning-to-USB-C cables. They draw power, but it's important to note that it's a negligible amount.

Here's a genuine Apple cable plugged into a power bank. Note that there's nothing plugged into the other end.

Genuine Apple cable

But it's not just the cables that Apple makes.

Here's a third-party cable.

Third-party Lightning-to-USB-C cable 

Here's another third-party cable, this one has a glowing LED in the connector, and while the power consumption is still really low, that glowing LED more than doubles the amount of power the cable draws.

Lightning-to-USB-C cable featuring LED

Another culprit is Apple's charge cable for the Apple Watch. There draws significantly more power, but in the grand scheme of things, it's still a negligible amount.

Apple Watch charger

Compare this to the power drawn by the AirPods Pro when charging, which is more than 10 times what the idle Apple Watch charging pad draws.

AirPods Pro charging

So, if this power draw is negligible, what's the problem?

The problem isn't so much the power consumption, but the fact that the cables keep the power banks in a powered-up state and prevent them from entering that low-power sleep state.

Note that this only happens for power banks that are designed to switch on and stay on with low-power devices. Some power banks won't even respond to these sorts of power draws, while others might turn on but will then switch off if the power consumption stays low (these usually do the same when charging low-power items such as earbuds).

It's also worth pointing out that USB-C to USB-C cables don't do this (with the exception of ones that have LEDs built into them, which will draw about the same as a Lightning-to-USB-C cable).

Also:Using the wrong USB-C cable can damage your tech. Here's how to avoid that

How quickly this depletes your power bank depends on its capacity. Small ones can be dead in a few days, bigger ones might last weeks or even longer.

But remember, that power bank is on the whole time, and not only is the battery being depleted, but it's also drawing power and also heating up.

And that heating up bit makes this bad news if you pack your power bank into a bag with the cables attached.

I hate to admit it, but I did this, throwing it into a suitcase, and when I found the power bank a few days later it was quite hot to the touch.

That could have ended badly.

Bottom line, unplug cables when not in use. Not only can that prevent these sorts of unexpected power draws, but it also reduces the chances of the ports or connectors suffering accidental damage.

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