Today, Samsung announced the new Galaxy S7 and Galaxy S7 Edge devices. For their 2016 flagships, Samsung increased the battery capacity of the flagship devices and these two handsets have the largest ever batteries of the Galaxy S range. The Galaxy S7 comes with a 3,000 mAh battery to keep the 1440p 5.1-inch AMOLED screen alive and the Galaxy S7 Edge has a 3,600 mAh battery and a 5.5-inch display. When it comes to charging, the Galaxy S7 family is well equipped: both devices come with Powermat and Qi wireless charging compatibility plus of course a USB port for wired charging. In addition to providing two different means of charging the device, Samsung have also given the handset two different charging modes: fast charging is now optional and may be toggled in the settings.
On the face of it, fast charging is arguably one of the most important breakthroughs in battery technology in recent years. Batteries have become more and more energy dense, that is for a given volume they can contain a higher capacity. However, this aspect of battery technology has been progressing slowly. Where fast charging comes into the equation is that the manufacturer accepts that the battery capacity is never going to be good enough, but the issue with including a very large battery is that it takes longer to recharge over a traditional USB cable. Fast charging allows the battery to soak up considerably more energy over a brief period and so is ideal for when we arrive home and are going out only a few minutes later, but our smartphone battery is looking a little low. Whilst we are getting changed, our device spends time on the charger and in those precious minutes, tops up the battery. Fast charging technologies only operate when the battery is discharged, and in the case of the Galaxy S6, only when the screen is off. The technology generates a lot of heat and in the case of Samsung's fast wireless charger, noise - Samsung use an active cooling system for their high performance wireless charger, as the notes attached to the option to toggle fast wireless charging state: "Charge your battery faster. You may hear a fan noise while using Fast charging. If Fast charging is off, standard wireless charging will be used instead."
There are a couple of reasons why one might disable fast charging, then: heat and noise. Heat is the enemy of batteries: the hotter the battery, the more readily it will break down. For the customer worried about the life of a fixed battery in the device, or caring for the environment and not wanting to discard an old, worn out battery unnecessarily, disabling fast charging should extend the useful life of the battery although it is not certain by how much longer it will improve things. As for noise, if the fast wireless charger were placed next to a bed, the whirring fan could be distracting.