A portable phone charger is the gift that keeps on giving because teenage boys will use it constantly and actually appreciate having it. Quality chargers hold their capacity better and charge more efficiently than cheap alternatives. Fast charging matters because he will want to top up quickly rather than wait around. The capacity should be decent enough to provide at least a full charge. The design should be compact enough to actually fit in a pocket or bag rather than being so large it becomes burdensome. Colours should be practical neutrals. A good portable charger is genuinely useful and he will notice the quality of construction when he is charging his phone for the tenth time that day.