Anker Nano Power Bank (30W, Built-In USB-C)

The least glamorous gift here is also the one most likely to be used daily. Teenagers run their phones flat and never have a cable, and this Anker solves both: a fold-out USB-C connector is built into the body, so it plugs straight into a phone with nothing to lose. The 10,000mAh capacity is good for roughly two full phone top-ups, and 30W output charges quickly and can even trickle-help a tablet. It is a touch chunkier and heavier than a bare battery because of the built-in plug, and it will not fast-charge a laptop, but as a stocking filler or add-on to a bigger present it is close to foolproof. One practical note: at 10,000mAh it is fine to carry onto a plane in hand luggage, unlike the bulkier packs. Reliable, useful and cheap enough to buy without a second thought.