question: Charging speeds. How come some devices will take a 90% charge in 5 minutes and 6 hours for the remaining 10%? (exaggeration)
comment: Physics is the answer. & #x200B; The physical world likes to balance things out. The greater the imbalance, the faster it tries to correct it. & #x200B; When charging batteries, this takes the form of electrons and voltage. As you use your cell phone, the cells inside the battery lose voltage. & #x200B; The charger outputs a fixed voltage. So when you run your battery down low, and then go to charge it, there is a *big* difference in the voltage level of the battery cells compared to the charger. This means lots of current will flow, your battery will charge quickly, and everything will get pretty warm. & #x200B; As the battery charges, the voltage level of the cells rises and gets closer to the voltage level of the charger. This causes things to slow down.
passages: BULLET::::- Capacity in mAh: mAh stands for milli Ampere-hour and measures the amount of power flow that can be supplied by a certain power bank at a specific voltage. Many manufacturers rate their products at 3.7 V, the voltage of cell(s) inside. Since USB outputs at 5 V, calculations at this voltage will yield a lower mAh number. For example, a battery pack advertised with a 3000 mAh capacity (at 3.7 V) will produce 2220 mAh at 5 V. Power losses due to efficiency of the charging circuitry also occur.
   Some companies have been experimenting with battery swapping to eliminate delay while charging.A “Super Fast” charging location will currently charge most cars to around 80% in 45–50 minutes.  The final 20% – as with a mobile phone – takes longer, because the systems slow to safely fill the battery and avoid any risks.
  
  Section::::Batteries.:Charging.:Hybrid vehicles.
  
  Some electric vehicles have built in generators, these are considered a type of hybrid vehicle. 
  
  Section::::Batteries.:Lifespan.
   The charging time depends on the battery capacity and the charging power. In simple terms, the time rate of charge depends on the charging level used, and the charging level depends on the voltage handling of the batteries and charger electronics in the car. The US based SAE International defines Level 1 (household 120V AC) as the slowest, Level 2 (upgraded household 240 VAC) in the middle and Level 3 (super charging, 480V DC or higher) as the fastest. Level 3 charge time can be as fast as 30 minutes for an 80% charge, although there has been serious industry competition about whose standard should be widely adopted. Charge time can be calculated using the formula: "Charging Time [h] = Battery Capacity [kWh] / Charging Power [kW]"
   Quick Charge was announce in 2012 and has more faster technology in 2016 using USB-C and USB-PD connector. It can charge mobile phone 4 times faster than standard micro USB.
  
  Section::::Applications.:Stationary battery plants.
   When a device doesn't recognize the faster-charging standard, generally the device and the charger fallback to the USB battery-charging standard of 5 V at 1.5 A (7.5 W).
  
  When a device detects it is plugged into a charger with a compatible faster-charging standard, the device pulls more current or the device tells the charger to increase the voltage or both to increase power (the details vary between standards).
  
  Such standards include:
  
  BULLET::::- Qualcomm Quick Charge
  
  BULLET::::- MediaTek Pump Express
  
  BULLET::::- Samsung Adaptive Fast Charging
  
  BULLET::::- Oppo Super VOOC Flash Charge, also called OnePlus Dash Charge
  
  BULLET::::- Huawei SuperCharge
   Chargers take from a few minutes to several hours to charge a battery. Slow "dumb" chargers without voltage or temperature-sensing capabilities will charge at a low rate, typically taking 14 hours or more to reach a full charge. Rapid chargers can typically charge cells in two to five hours, depending on the model, with the fastest taking as little as fifteen minutes. Fast chargers must have multiple ways of detecting when a cell reaches full charge (change in terminal voltage, temperature, etc.) to stop charging before harmful overcharging or overheating occurs. The fastest chargers often incorporate cooling fans to keep the cells from overheating. Battery packs intended for rapid charging may include a temperature sensor that the charger uses to protect the pack; the sensor will have one or more additional electrical contacts.
   Quick Charge is a proprietary technology which allows for the charging of battery powered devices, primarily mobile phones, at levels above and beyond the typical 5 volts and 2 amps for which most USB standards allow. Numerous other companies have their own competing technologies; these include Mediatek's Pump Express, OPPO's VOOC (licensed to OnePlus as Dash Charge). To take advantage of Qualcomm Quick Charge, both the host providing power and the device must support it. In 2012 the USB Implementers Forum (USB IF) announced that their USB Power Delivery (USB PD) standard had been finalized which allows for devices to transfer up to 100 watts of power over capable USB ports. This new technology was first seen in a Xiaomi Mi Mix 3 prototype that went from 1% to 100% in a mere 17 minutes.
   Charging stations can have a variety of different speeds of charging, with slower charging being more common for houses, and more powerful charging stations on public roads and areas for trips. The BMW i3 can charge 0–80% of the battery in under 30 minutes in rapid charging mode. The superchargers developed by Tesla Motors provided up to 130 kW of charging, allowing a 300-mile charge in about an hour.
  
  Section::::Infrastructure.:Charging station.:Connectors.
   A 10 amp-hour battery could take 15 hours to reach a fully charged state from a fully discharged condition with a 1 amp charger as it would require roughly 1.5 times the battery's capacity.
  
  Public EV charging stations provide 6 kW (host power of 208 to 240 VAC off a 40 amp circuit). 6 kW will recharge an EV roughly 6 times faster than 1 kW overnight charging.
  
  Rapid charging results in even faster recharge times and is limited only by available AC power, battery type, and the type of charging system.
   A patent filed by the corporation, published in late July 2013, revealed the development of a new iPhone battery system that uses location data in combination with data on the user's habits to moderate the handsets power settings accordingly. Apple is working towards a power management system that will provide features such as the ability to estimate the length of time a user will be away from a power source to modify energy usage and a detection function that adjusts the charging rate to best suit the type of power source that is being used.
  
  Section::::Hardware.:Battery.:Controversy.
   Charging times vary depending on the battery pack's state-of-charge, its overall capacity, the available voltage, and the available circuit breaker amperage. From a 120 volt/15 amp household outlet, the range increases by for every hour of charging. From a , NEMA 14–50 240 V/50 A outlet (like those used by RVs or standard cooking ranges), the charge rate is per hour. Using Tesla's , High Power Wall Connector increases the rate to per hour if the car is configured with dual chargers ().
  
  Section::::Design.:Charger.:Europe/Asia-Pacific.
   For example, for a battery with a capacity of 500 mAh, a discharge rate of 5000 mA (i.e., 5 A) corresponds to a C-rate of 10 (per hour), meaning that such a current can discharge 10 such batteries in one hour. Likewise, for the same battery a charge current of 250 mA corresponds to a C-rate of 1/2 (per hour), meaning that this current will increase the state of charge of this battery by 50% in one hour.
   A patent filed in July 2013 revealed the development of a new iPhone battery system that uses location data in combination with data on the user's habits to moderate the handsets power settings accordingly. Apple is working towards a power management system that will provide features such as the ability of the iPhone to estimate the length of time a user will be away from a power source to modify energy usage and a detection function that adjusts the charging rate to best suit the type of power source that is being used.
   Before the Battery Charging Specification was defined, there was no standardized way for the portable device to inquire how much current was available. For example, Apple's iPod and iPhone chargers indicate the available current by voltages on the D− and D+ lines. When D+ = D− = 2.0 V, the device may pull up to 900 mA. When D+ = 2.0 V and D− = 2.8 V, the device may pull up to 1 A of current. When D+ = 2.8 V and D− = 2.0 V, the device may pull up to 2 A of current.
  
  Section::::Power.:USB Battery Charging.:Accessory charging adaptors (ACA).
   In 2005, handheld device battery designs by Toshiba were claimed to be able to accept an 80% charge in as little as 60 seconds. Scaling this characteristic up to the same 7 kilowatt-hour EV pack would result in the need for a peak of 340 kilowatts of power from some source for those 60 seconds. It is not clear that such batteries will work directly in BEVs as heat build-up may make them unsafe.
  
  Section::::Specifics.:Charging.:Recharging time.
  
  Electric cars like Tesla Model S, Renault Zoe, BMW i3, etc. can recharge their batteries at quick charging stations within 30 minutes to 80 percent.
   Battery charging and discharging rates are often discussed by referencing a "C" rate of current. The C rate is that which would theoretically fully charge or discharge the battery in one hour. For example, trickle charging might be performed at C/20 (or a "20 hour" rate), while typical charging and discharging may occur at C/2 (two hours for full capacity). The available capacity of electrochemical cells varies depending on the discharge rate. Some energy is lost in the internal resistance of cell components (plates, electrolyte, interconnections), and the rate of discharge is limited by the speed at which chemicals in the cell can move about. For lead-acid cells, the relationship between time and discharge rate is described by Peukert's law; a lead-acid cell that can no longer sustain a usable terminal voltage at a high current may still have usable capacity, if discharged at a much lower rate. Data sheets for rechargeable cells often list the discharge capacity on 8-hour or 20-hour or other stated time; cells for uninterruptible power supply systems may be rated at 15 minute discharge.
   Slow battery chargers may take several hours to complete a charge. High-rate chargers may restore most capacity much faster, but high rate chargers can be more than some battery types can tolerate. Such batteries require active monitoring of the battery to protect it from overcharging. Electric vehicles ideally need high-rate chargers. For public access, installation of such chargers and the distribution support for them is an issue in the proposed adoption of electric cars.
  
  Section::::C-rate.
   Ni–Cd batteries can be charged at several different rates, depending on how the cell was manufactured. The charge rate is measured based on the percentage of the amp-hour capacity the battery is fed as a steady current over the duration of the charge. Regardless of the charge speed, more energy must be supplied to the battery than its actual capacity, to account for energy loss during charging, with faster charges being more efficient. For example, an "overnight" charge, might consist of supplying a current equal to one tenth the amperehour rating (C/10) for 14–16 hours; that is, a 100 mAh battery takes 10 mA for 14 hours, for a total of 140 mAh to charge at this rate. At the rapid-charge rate, done at 100% of the rated capacity of the battery in 1 hour (1C), the battery holds roughly 80% of the charge, so a 100 mAh battery takes 125 mAh to charge (that is, approximately 1 hour and fifteen minutes). Some specialized batteries can be charged in as little as 10–15 minutes at a 4C or 6C charge rate, but this is very uncommon. It also greatly increases the risk of the cells overheating and venting due to an internal overpressure condition: the cell's rate of temperature rise is governed by its internal resistance and the square of the charging rate. At a 4C rate, the amount of heat generated in the cell is sixteen times higher than the heat at the 1C rate. The downside to faster charging is the higher risk of overcharging, which can damage the battery. and the increased temperatures the cell has to endure (which potentially shortens its life).
   Prior to Power Delivery, mobile phone vendors used custom protocols to exceed the 7.5 W cap on USB-BCS. For example, Qualcomm's Quick Charge 2.0 is able to deliver 18 W at a higher voltage, and VOOC delivers 20 W at the normal 5 V. Some of these technologies, such as Quick Charge 4, eventually become compatible with USB PD again.
  
  Section::::Power.:Sleep-and-charge ports.
   Control Pilot (Current limit): The charging station can use the wave signal to describe the maximum current that is available via the charging station with the help of pulse width modulation: a 16% PWM is a 10 A maximum, a 25% PWM is a 16 A maximum, a 50% PWM is a 32 A maximum and a 90% PWM flags a fast charge option.
   Both phones have a large 4,000 mAh battery with fast charging. Huawei claims that the phone can be charged from 1 to 20 percent in 10 minutes, and from 1 to 58 percent in 30 minutes.
   The limit to device power draw is stated in terms of a "unit load", which is 100 mA or 150 mA for SuperSpeed devices. Low-power devices may draw at most 1 unit load, and all devices must act as low-power devices before they are configured. High-power devices draw at most 5 unit loads (900 mA) or 6 unit loads (1200 mA) for SuperSpeed devices. A high-powered device must be configured, and may only draw as much power as specified in its configuration. I.e., the maximum power may not be available.
   Per the base specification, any device attached to a "standard downstream port" (SDP) must initially be a low-power device, with high-power mode contingent on later USB configuration by the host. Charging ports, however, can immediately supply between 0.5 and 1.5 A of current. The charging port must not apply current limiting below 0.5 A, and must not shut down below 1.5 A or before the voltage drops to 2 V.
   The current drawn by typical constant-voltage energy distribution systems is usually dictated by the power (watt) consumed by the system and the operating voltage. For this reason the examples given below are grouped by voltage level.
  
  Section::::Everyday examples.:CPUs – 1 V DC.
  
  BULLET::::- Current notebook CPUs (up to 15...45 W at 1 V): up to 15...45 A
  
  BULLET::::- Current high-end CPUs (up to 65...140 W at 1.15 V): up to 55...120 A
  
  Section::::Everyday examples.:Portable devices.
  
  BULLET::::- Hearing aid (typically 1 mW at 1.4 V): 700 µA
  
  BULLET::::- USB charging adapter (as power supply – typically 10 W at 5 V): 2 A
   BULLET::::- Simultaneous charging and discharging: need to specify if the powerbank can be used while it is charging.
  
  BULLET::::- Number of output USB ports: This specifies the number of devices that can be charged simultaneously.
  
  BULLET::::- Output current rating: This specifies the current rating that it can charge maximum. The higher the number, the better the powerbank. This can vary from output port to output port. Also, some powerbanks don’t have dedicated high current ports, but will drop the output at all ports if the maximum total current output of the powerbank is exceeded.
  
raw_presuppositions: Devices should charge linearly.
raw_corrections: As a battery charges, the voltage level of the cells gets closer to the voltage level of the charger, which causes charging to slow down.