question: How does fast charging work? And why does it sometimes fast charge first try and other times it needs to be replugged in?
comment: So, to start, we have to consider the usual standard: USB 2.0 is designed to provide a potential difference of five volts at a current of 500 milliamps. That's not an awful lot of power in the scheme of things, and that translates to taking a long time to charge. Enter fast charging (called Quick Charge by Qualcomm, and other names by other companies). Fast-charging is a technology where a compatible phone and charger "talk" to each other and agree on a higher voltage and/or amperage that both devices can tolerate without risking damage to either. If it needs to be plugged in again to recognize Quick Charge, that means that the data lines didn't make good enough contact for the two pieces to connect.
passages: 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
   Section::::Type.:Fast charger.
  
  Fast chargers make use of control circuitry to rapidly charge the batteries without damaging any of the cells in the battery. The control circuitry can be built into the battery (generally for each cell) or in the external charging unit, or split between both. Most such chargers have a cooling fan to help keep the temperature of the cells at safe levels. Most fast chargers are also capable of acting as standard overnight chargers if used with standard NiMH cells that do not have the special control circuitry.
  
  Section::::Type.:Three stage charger.
   Quick Charge
  
  Quick Charge is a technology found in Qualcomm SoCs, used in devices such as mobile phones, for managing power delivered over USB. It offers more power and thus charges batteries in devices faster than standard USB rates allow. Quick Charge 2 onwards technology is primarily used for wall adaptors, but it is also implemented in car chargers and powerbanks (For both input and output power delivery). 
  
  Section::::Details.
   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 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.
   In order to prevent cell damage, fast chargers must terminate their charge cycle before overcharging occurs. One method is to monitor the change of voltage with time. When the battery is fully charged, the voltage across its terminals drops slightly. The charger can detect this and stop charging. This method is often used with nickel–cadmium cells, which display a large voltage drop at full charge. However, the voltage drop is much less pronounced for NiMH and can be non-existent at low charge rates, which can make the approach unreliable.
   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.
   Until 2013, there was an issue where Blink chargers were overheating and causing damage to both charger and car. The solution employed by the company was to reduce the maximum current.
  
  Section::::Deployment of public charging stations.
   Another standards organization, The International Electrotechnical Commission, defines charging in "modes" (IEC 62196).
  
  BULLET::::- "Mode 1" – slow charging from a regular electrical socket (single- or three-phase)
  
  BULLET::::- "Mode 2" – slow charging from a regular socket but with some EV specific protection arrangement (e.g., the Park & Charge or the PARVE systems)
  
  BULLET::::- "Mode 3" – slow or fast charging using a specific EV multi-pin socket with control and protection functions (e.g., SAE J1772 and IEC 62196)
  
  BULLET::::- "Mode 4" – fast charging using some special charger technology such as CHAdeMO
  
  There are three connection "cases":
   For faster charging, dedicated chargers can be built in permanent locations and provided with high-current connections to the grid. In this style of connection, the charger's DC output has no effective limit, theoretical or practical. Such high voltage and high-current charging is called a DC fast charge (DCFC) or DC quick charging (DCQC).
   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.
   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]"
   BULLET::::- Heating of the socket and cables following intensive use for several hours at or near the maximum power (which varies from 8 to 20 A depending on the country).
  
  BULLET::::- Fire or electric injury risks if the electrical installation is obsolete or if certain protective devices are absent.
  
  The second limitation is related to the installation's power management.
  
  BULLET::::- As the charging socket shares a feeder from the switchboard with other sockets (no dedicated circuit) if the sum of consumptions exceeds the protection limit (in general 16 A), the circuit-breaker will trip, stopping the charging.
   CHAdeMO has recently unveiled its new protocol for 400 kW ‘ultra-fast’ charging. The new 'CHAdeMO 2.0', delivering a 400 kW output, will allow the standard to better compete with the latest CCS “ultra-fast” stations currently being built around the world as part of new networks such as IONITY charging consortium.
  
  Section::::Deployment.:In charging stations.:West Coast Electric Highway.
  
  The West Coast Electric Highway (WCEH) is an extensive network of electric vehicle (EV) DC fast charging stations located every 25 to 50 miles along Interstate 5 and other major roadways in the Pacific Northwest of the United States.
   BULLET::::- Charging systems may attempt to gauge battery string capacity by measuring overall voltage. Due to the overall string voltage depletion due to the dead cells, the charging system may detect this as a state of discharge, and will continuously attempt to charge the series-parallel strings, which leads to continuous overcharging and damage to all the cells in the degraded series string containing the damaged battery.
   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 variant of CC/CV charging algorithms is the further development of the constant CC/CV. The boost charger（BC) is one of them. Instead of using the constant voltage and current in the entire charging period, the BC is to boost the charging efficiency through maximizing the voltage in the first period, and the charging capacity could reach 30% of its nominal capacity approximately. After this period, the charging algorithm is then switched to the standard CC/CV. Due to the initial higher charging voltage, the BC-CC/CV can charge the battery faster than the CC/CV, but it is required to fully discharge the battery before charging which requires the discharge circuit. While this algorithm will increase the number of components and costs. As the charger is needed to be variant in the voltage, all components need to afford the voltage, contemporary. The necessity of discharge before charging is important as this will influence the efficiency charging algorithm and the lifecycle of batteries. According to the statistical result of a survey on the effect of the initial higher charging voltage on the battery life has been investigated. It shows that there is no obvious degradation within 500 testing cycles. 
   "AC Level 3" charging was defined in early editions of SAE J1772 at up to 400 amps, but has been dropped. Edition 7 of J1772 (2017) states in Appendix M "AC Level 3 charging has never been implemented. The following is historical information for reference only." The term "Level 3" appears to have been adopted colloquially to mean DC "fast" charging, although "Level 3" was never defined to mean that in J1772. Table 17 in Appendix M of J1772 (2017) lists AC Level 2 and AC Level 3 from 208 to 240 VAC, and DC Charging with 208-600 V input and 0–1000 V DC output.
   BULLET::::- Compatible standards – Not all devices are compatible with different inductive chargers. However, some devices have started to support multiple standards.
  
  BULLET::::- Inefficiency – Inductive charging is not as efficient as direct charging. In one application, the phone being charged gets hot. Continued exposure to heat can result in battery damage.
   Smart charging
  
  Smart charging is a form of electric vehicle charging in which the time and rate at which an EV's battery pack is charged can be controlled in a more "intelligent" way than the simple use of a manual on/off switch.
  
  Typically smart charging is used to reduce the peak loads on the electricity distribution grid supplying the power needed to charge an electric vehicle.
  
  The United Kingdom Government has mandated that:
   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.
   In the United States, Aker Wade Power Technologies has entered into a licensing agreement with TEPCO to manufacture and market DC fast chargers for electric vehicles. Eaton Corporation has demonstrated a CHAdeMO-compatible DC quick charger recharging Mitsubishi iMiEV cars. ECOtality has deployed the Blink DC Fast Charger, which is outfitted with two CHAdeMO-compliant electric vehicle charging connectors, in the Blink Network. AeroVironment offers a broad line of DC fast chargers including two CHAdeMO certified Quick Charger models. Princeton Power Systems' UL-certified (2202 and 1741) bi-directional CHAdeMO charger fast-charger is capable of charging and discharging from the Nissan LEAF, for both grid-tied and backup-power modes. The fast-chargers are available in 10 kW, 15 kW, and 30 kW sizes.
   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.
   Fast charging, however and whenever it gets built out, is going to be key for the development of a mainstream market for plug-in electric vehicles. The broader conflict between the CHAdeMO and SAE Combo connectors, we see that as a hindrance to the market over the next several years that needs to be worked out.
  
  As of September 16, 2013, a standard does not exist in Australia for charging connectors. Australia’s first fast-DC charging stations follow the Japanese CHAdeMO standard.
  
  Section::::Standards.:EV charging station signs.
   Maxim Integrated touts a combined voltage and charge approach that is claimed superior to either method alone; it is implemented in their ModelGauge m3 series of chips, such as MAX17050, which is used in the Nexus 6 and Nexus 9 Android devices, for example.
  
  Section::::Determining SoC.:Kalman filtering.
  