question: Why is it that the first 10-20% of most IPhone battery’s are used up within the first 20-30 minutes while the last percent can sometimes last up to 15-20 minutes?
comment: Two things are happening. First, it is not easy to tell how charged a battery is. The only thing you can really tell from a battery is the voltage. From that, and previous study of the battery, software in the phone and the battery can estimate the remaining charge. Secondly, as the charge in the battery gets low, the phone switches of bits of functionality to make it last longer.
passages: 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.
   Battery consumption of the phones is a factor that must be taken into account when deploying beacon-enabled apps. A recent report has shown that
  
  older phones tend to draw more battery in the vicinity of iBeacons, while the newer phones can be more efficient in the same environment. In addition to the time spent by the phone scanning, number of scans and number of beacons in the vicinity are also significant factors for battery drain, as pointed out by the Aislelabs report. 
   In February 2017, Apple released a statement to "TechCrunch", saying that the iOS 10.2.1 update, released on January 23, had reduced the occurrence of battery shutdowns by "more than 80%" on iPhone 6S devices.
  
  On December 28, 2017, Apple decreased the price of an out-of-warranty battery replacement for iPhone 6 or later from $79 to $29 for one year until December 31, 2018, and promised an iOS update that would provide more information about an iPhone's battery health which eventually turned out to be iOS 11.3.
  
  Section::::See also.
  
  BULLET::::- List of iOS devices
  
  BULLET::::- History of iPhone
   "The Next Web"s Juan Buis wrote in late November 2016 that "complaints are shared [on Apple's support forums] about various iPhone models turning off when the battery falls below a certain percentage", and blames the iOS 10.1.1 update. He further wrote that "the original post [on support forums] explains that the phone dies when there’s 30 percent charge left, and many others have since replied that they’re experiencing the same." iOS 10.2, released in December 2016, adds a telemetry diagnostic tool that Apple can use to report battery consumption, for diagnosing reported issues with 30% battery shutdowns. In February 2017, Apple released a statement to "TechCrunch", saying that the iOS 10.2.1 update, released on January 23, had reduced the occurrence of battery shutdowns by "more than 80%" on iPhone 6S devices and "over 70%" on iPhone 6 devices. In full, the statement read:
   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.
   In December 2016, Apple revealed new details about the issue, stating that the affected devices contained a "battery component that was exposed to controlled ambient air longer than it should have been before being assembled into battery packs". The statement also said that customers "outside of the affected range" may also experience unexpected shutdowns, though clarifying that some shutdowns can occur under "normal conditions" because the iPhone tries to "protect its electronics". They provided a highly discounted battery replacement to customers for a year. Apple also said that an upcoming update to the iOS operating system would include additional diagnostic tools to help Apple find more information about different kinds of battery issues.
   Apple Inc. clarifies that a charge cycle means using all the battery's capacity, but not necessarily by discharging it from 100% to 0%: "You complete one charge cycle when you’ve used (discharged) an amount that equals 100% of your battery’s capacity — but not necessarily all from one charge. For instance, you might use 75% of your battery’s capacity one day, then recharge it fully overnight. If you use 25% the next day, you will have discharged a total of 100%, and the two days will add up to one charge cycle."
  
  Section::::See also.
  
  BULLET::::- Deep cycle battery
   Where E is the rated battery energy capacity and SOD (Vi) is the battery state of discharge at voltage Vi and P is the average power consumption in the time interval t1 and t2. The state of discharge can be estimated using look up table where the relationship between present voltage and SOD is captured. Determining the energy is also an issue because the energy is changing as the battery gets old. The new batteries have the total energy written on their back but the value can’t be true for all time. It can estimate the energy at highest and lowest discharge rate to decrease the error. The internal resistance also has significant impact on the discharged current. To decrease the effect of internal resistance all the phone components can be switched to their lowest power modes to minimize the discharge current when taking a voltage reading. Finally, this method uses a piece-wise linear function to model the non-linear relationship between SOF and battery voltage.
   Apple runs tests on preproduction units to determine battery life. Apple's website says that the battery life "is designed to retain up to 80% of its original capacity after 400 full charge and discharge cycles", which is comparable to iPod batteries.
  
  The battery life of early models of the iPhone has been criticized by several technology journalists as insufficient and less than Apple's claims. This is also reflected by a J. D. Power and Associates customer satisfaction survey, which gave the "battery aspects" of the iPhone 3G its lowest rating of two out of five stars.
   Within a week of the launch of the 11.3.1 update, users began reporting continued issues with this update regarding battery drainage. Some of these reports indicated drains from 57% down to 3% in just 3 minutes. Even users with the health of the battery measuring 96% noticed iPhones draining at around 1% per minute. In addition to battery drains, some iPhone users noticed their devices having excessive heat buildup.
  
  It has been recommended by technology experts that users not upgrade their software until the release of a version subsequent to 11.3.1 unless specifically plagued by the 'third party display issue'.
   On December 28, 2017, amidst many complaints about older iPhone models slowing down when new ones are released, Apple released a communication to its customers on its website, acknowledging the effect that old batteries have on the iPhone's performance. The company offered $29 battery replacements as a solution.
  
  Section::::Hardware.:Camera.
   In a follow-up report, Aislelabs found a drastic improvement in battery consumption for iPhone5S, iPhone 5C versus the older model iPhone 4S.
  
  At 10 surrounding iBeacons, iPhone 4S can consume up to 11% of battery per hour whereas iPhone5S consumes a little less than 5% battery per hour.
  
  An energy efficient iBeacon application needs to consider these aspects in order to strike a good balance between app responsiveness and battery consumption.
  
  Section::::History and developments.
   In November 2016, Apple announced that a "very small number" of iPhone 6S devices manufactured between September and October 2015 have faulty batteries that unexpectedly shut down. While Apple noted that the battery problems were "not a safety issue", it announced a battery replacement program for affected devices. Customers with affected devices, which span "a limited serial number range", were able to check their device's serial number on Apple's website, and, if affected, receive a battery replacement free of charge at Apple Stores or authorized Apple Service Providers.
   Section::::Problems.:Battery drain.
  
  Adrian Kingsley-Hughes of "ZDNet" wrote in March 2014 that iPhone and iPad users reported battery drain with the iOS 7.1 update. In lab testing, Andrew Cunningham of "Ars Technica" found some hardware models experienced minor battery depletion, while others experienced no statistically significant changes.
  
  Section::::Problems.:Lock screen bypass.
  
  Dom Esposito of "9to5Mac" reported in June 2014 that a new lock screen bypass method had been discovered in iOS 7, allowing access to the phone in "5 seconds under certain circumstances". The issue was later fixed.
  
  Section::::Hoaxes.
   Battery consumption of the phones is a factor that must be taken into account when deploying beacon enabled apps. A recent report has shown that
  
  older phones tend to draw more battery power in the vicinity of iBeacons, while the newer phones can be more efficient in the same environment. In addition to the time spent by the phone scanning, number of scans and number of beacons in the vicinity are also significant factors for battery drain, as pointed out by the Aislelabs report. 
   Batterygate
  
  Batterygate is a controversy over Apple Inc.'s use of software upgrades to slow down Apple devices, supposedly in order to prolong their battery life.
  
  Section::::History.
  
  Due to reports of iPhones shutting off with around 30% battery life on the iPhone 6, iPhone 6s and iPhone SE , Apple released iOS 10.2.1 which secretly throttled the CPU performance of the iPhone 6, iPhone 6s and iPhone SE with older batteries. Other iPhone models are not affected by this problem and so have no need to be throttled.
   There was intended to be no significant difference in performance between the parts, but in October 2015, it was alleged that iPhone 6S models with Samsung-fabricated A9 chips consistently measured shorter battery life than those with TSMC-fabricated versions in CPU heavy usage; web browsing and graphics were not very different. Apple responded that "tests which run the processors with a continuous heavy workload until the battery depletes are not representative of real-world usage", and said that internal testing combined with customer data demonstrated a variance of only 2–3%.
  
  Section::::Design.:Naming.
   The iPhone's indicators are more exposed than those in some mobile phones from other manufacturers, which carry them in a more protected location, such as beneath the battery behind a battery cover. These indicators can be triggered during routine use, by an owner's sweat, steam in a bathroom, and other light environmental moisture. Criticism led Apple to change its water damage policy for iPhones and similar products, allowing customers to request further internal inspection of the phone to verify if internal liquid damage sensors were triggered.
  
  Section::::Hardware.:Included items.
   Users started reporting battery drain issues after the February security update. The battery drain become worse after the April security updates. Google is looking for a fix.
  
  Users are reporting proximity sensor issues. Google is aware of the issue and looking for a fix.
  
  Some users are having issues making calls and receiving MMS messages. Google claims these issues are fixed but users are still complaining about them.
   In a follow up report, Aislelabs found a drastic improvement in battery consumption for iPhone5S, iPhone 5C versus the older model iPhone 4S.
  
  At 10 surrounding iBeacons, iPhone 4S can consume up to 11% of battery per hour whereas iPhone5S consumes a little less than 5% battery per hour.
  
  An energy efficient iBeacon application needs to consider these aspects in order to strike a good balance between app responsiveness and battery consumption.
  
  Section::::Design.:USB powered.
   A BMS may monitor the state of the battery as represented by various items, such as:
  
  BULLET::::- Voltage: total voltage, voltages of individual cells, minimum and maximum cell voltage or voltage of periodic taps
  
  BULLET::::- Temperature: average temperature, coolant intake temperature, coolant output temperature, or temperatures of individual cells
  
  BULLET::::- State of charge (SOC) or depth of discharge (DOD), to indicate the charge level of the battery
  
  BULLET::::- State of health (SOH), a variously-defined measurement of the remaining capacity of the battery as % of the original capacity
   iOS 9 comes with two important battery-saving updates. When a phone has been placed face-down, the screen will not light up upon receiving notifications. Apple has also added Low Power Mode, which modifies the amount of energy dedicated to background services and animations. For example, background app refresh and push email are paused during Low Power Mode. When a phone reaches 20% battery level, users are automatically prompted to turn on Low Power Mode, which changes the color of the battery icon in the top row status bar on the screen to yellow. When the battery goes higher than the 80% level, Low Power Mode automatically turns back off.
   Section::::Problems.:Battery shutdowns.
   In use, the voltage across the terminals of a disposable battery driving a load decreases until it drops too low to be useful; this is largely due to an increase in internal resistance rather than a drop in the voltage of the equivalent source.
  
  In rechargeable lithium polymer batteries, the internal resistance is largely independent of the state of charge but increases as the battery ages; thus, it is a good indicator of expected life.
  
  Section::::See also.
  
  BULLET::::- Norton's theorem
  
  Section::::References.
  
  BULLET::::- Student Reference Manual for Electronic Instrumentation Laboratories (2nd Edition) - Stanley Wolf & Richard F.M. Smith
   Some users have experienced battery drain problems after updating to iOS 11. In a poll on its website, 70% of "9to5Mac" visitors reported decreased battery life after updating to the new operating system. However, in an article featuring Twitter complaints of battery life, "Daily Express" wrote that "honestly, this is to be expected. It happens every year, and it's completely normal. Major iOS releases will hammer the battery on your device much faster during the first few days of use", with "Forbes" stating in an article that "The days after you install a new version of iOS, your iDevice is busy doing all sorts of housekeeping. Practically all of your apps have updates, so iOS is busy downloading and installing them in the background. [...] Additionally, after you install a new version of iOS, it has to do something called "re-indexing." During this process, iOS 11 will comb through all of the data on your device so that it can be cataloged for quick Spotlight searching." The article further states that "The good news is that both of these things are temporary".
  
raw_presuppositions: Phones show an accurate display of battery charge. . The charge level indicator on a phone is accurate.
raw_corrections: Phone software only estimates the remaining charge of a phones battery. The only thing you can really tell from a battery is the voltage, charge level of the battery is an estimate.