The USB spec requires the output voltage of USB power to be a certain voltage and regulated to a maximum current, which is lower if the device (such as a hub) transfers data and is higher if the device is built for charging (i.e. heavier wire and components) and has the data capability disabled. Higher capacity chargers use exactly the same voltage as lower rated ones and the battery draws the amount of current it needs based on its internal resistance. Higher capacity chargers can supply more current to larger batteries before the voltage drops below the spec, but they can easily supply the current needed by lower capacity batteries.
There is absolutely no danger of using a higher capacity USB power supply to charge a lower capacity battery. This is no different than using 150 mph rated tires at speeds no higher than 65 mph or a 100 pound person climbing a ladder rated for 300 pounds. OTOH, using too low of a current/wattage rated charger will at least charge the battery slowly, sometimes not at all, and could result in damage to the charger.
