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Home > Smart Living> Innovation > Fast charging in smartphones: how fast is quick enough?

Fast charging in smartphones: how fast is quick enough?

Many smartphone brands have breached triple-digit charging speeds in recent months. But here's why you should look past the numbers

Phones with 45W and 67W fast chargers are making way for 120W and 150W charging solutions, and 200W and 240W charging tech is waiting in the wings.
Phones with 45W and 67W fast chargers are making way for 120W and 150W charging solutions, and 200W and 240W charging tech is waiting in the wings. (iStock)

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Remember that quaint little habit called overnight charging? Not so long ago, one would plug in a phone at bedtime to ensure a fully charged phone when one woke up, ready for the day ahead. If you are moving up from a dated device with a bundled 5-watt (5W) charger, the promise of fast charging is particularly tantalising—plug in your phone for mere minutes to have it ready for another day of use.

Phones with 45W and 67W fast chargers are making way for 120W and 150W charging solutions, and 200W and 240W charging tech is waiting in the wings. This bigger-is-better move is reminiscent of the megapixel counts on smartphone cameras but, as with megapixels, is it mostly a matter of bragging rights?

Also read: Should you invest in a flagship phone?

Let’s put things in perspective. A phone’s ability to charge comes down to the highest wattage (W) supported by it, which is the product of voltage (Volts) and the current (Amperes). Typically, phones charge at 5V, 2A or 10W, so anything above this value is technically fast charging. Until a couple of years ago, you would have to shackle your phone to its charger for nearly three hours to top it from empty. The likes of the 55-67W chargers brought it down to 40-50 minutes.

Over the past six months, brands have breached triple-digit charging speeds, with 120W/150W chargers juicing up the 4,500-5,000mAh batteries in under 20 minutes, under ideal conditions. For most brands, these ideal conditions include switching on airplane mode, having no apps running in the background and keeping the phone in ambient temperatures of under 25 degrees Celsius. That 100W-plus charging speed becomes just a theoretical possibility if you want to use your phone while it’s charging. Even so, though, you do get around 80% of charge in 15 minutes and a fully topped-up phone in 30 minutes, in everyday conditions.

Bigger numbers are yet to come, with Vivo and Xiaomi announcing their own variants of 200W charging, and Oppo showcasing 240W SuperVOOC charging that charges a 4,500mAh battery in just nine minutes.

Look past the numbers

If you’re sold on the fast-charging gravy train, know this much – it is somewhat misleading. Just because a charger is labelled as a 120W or 150W charger doesn’t mean, however, that it delivers that wattage constantly (see the last section: The Tech Behind Fast Charging). This number on the box is the peak number, which can be splashed across marketing channels.

You would also need to weigh if the bumped-up price (see the section: Guilty As Charged below) is worth it for the little gains (of 10-15 minutes) you see in absolute charging times. The higher price goes towards better safety measures and certifications and, in some cases, smaller batteries. Compare the Xiaomi 11i HyperCharge, the Realme GT Neo 3 150W or the OnePlus 10R Endurance Edition to their sub-85W variants and you will find each packs smaller batteries.

Mind you, none of them claim better battery performance, which is a tangible user metric. Only faster charging.

The Xiaomi 12 Pro ( <span class='webrupee'>₹</span>62,999) packs in a 120W charger that juices up the 4,600mAh battery in around 20 minutes, which means you can game hard all day and be back up and running while you take a break.
The Xiaomi 12 Pro ( 62,999) packs in a 120W charger that juices up the 4,600mAh battery in around 20 minutes, which means you can game hard all day and be back up and running while you take a break. (Xiaomi)

Guilty as charged

Insanely fast charging isn’t limited to flagships smartphones, so if you’re looking to dip your feet into the fast-charging pool, here are some options to consider.

Premium flagships: The Xiaomi 12 Pro ( 62,999) packs in a 120W charger that juices up the 4,600mAh battery in around 20 minutes, which means you can game hard all day and be back up and running while you take a break. The iQOO 9 Pro beat Xiaomi to the post by launching the first Snapdragon 8 Gen 1 phone, 2K/120Hz display and gimbal stabilisation and all, with triple-figure (120W) charging speeds for its 4,700mAh battery.

Speed demons: The Realme GT Neo 3 150W ( 42,999) and the OnePlus 10R SuperVOOC Endurance Edition ( 43,999) both feature a 6.7-inch 120Hz AMOLED display, a MediaTek Dimensity 8100 chip (the 10R has a marginally higher spec-ced Max variant) and a similar triple camera setup. Both can stake claim to being the fastest spec-ced charging games in town with their 150W variants, which take the 4,500mAh batteries from empty to full in just over 20 minutes.

Budget flagships: The Xiaomi 11i HyperCharge ( 26,999) remains the most economical way of hopping on to the triple-digit charging train, with its 4,500mAh battery topping up in close to 20 minutes. Its pricier Xiaomi 11T Pro sibling ( 39,999) goes a step further by packing in a larger 5,000mAh battery and a Snapdragon 888 chip.

Fast(er) charging for the rest of us

You’re not going to get faster charging without picking up one of these blisteringly fast new devices, are you? That is not entirely true.

There are many small tips you can follow to optimally charge your older smartphone. For instance, always use the wall charger (ideally the one that came in the box with its original cable) for a charging speed best mated to your device—plugging your phone into your laptop is a sure-fire way of not charging fast. Of course, where possible (or if the brand hasn’t packed a charger), look up the fastest charging profile your phone supports and get a charger which matches that.

The other thing you can watch out for is heat—either in terms of the ambient temperatures where you are charging the phone, or playing heavy games while charging your phone. Both slow down the charging process to conserve battery life. For those dire moments when every drop of juice counts, switch to airplane mode, kill all background processes (or switch off the phone altogether) to get the most out of your charger.

The Xiaomi 11i HyperCharge ( <span class='webrupee'>₹</span>26,999) remains the most economical way of hopping on to the triple-digit charging train.
The Xiaomi 11i HyperCharge ( 26,999) remains the most economical way of hopping on to the triple-digit charging train. (Xiaomi)

The tech behind fast charging

To fully grasp how fast charging works, a primer is in order. Fast charging isn’t about throwing as much voltage and current at a smartphone battery as possible. In the first of a two-step process, the charger keeps a constant flow of current at a fixed amperage, and slowly increases the voltage until it reaches the phone’s peak voltage. From there on, the voltage is kept fixed, while the amperage is slowly decreased until the battery is fully charged.

The first phase is less detrimental to the long-term health of the phone battery, while the latter, coupled with heat, tends to impact the battery life more, and phone-charging algorithms optimise around this basic fact. As a result, you will see the pace of fast charging most in the first phase, when the battery is less than 50% full all the way up to around 80%. Past 75-80%, charging speeds drop off to conserve battery life, so much so that brands often claim their optimised charging algorithms and temperature checks (to adjust inflow based on ambient temperature) help maintain 80% of battery health even after 800 charge cycles. With the added risks that extreme fast-charging speeds add to the charging mix, brands use a combination of temperature sensors, overheating shutdown circuit protection measures, and dual-cell batteries with dual charge pumps to safely increase the input power when compared to a standard single-cell battery.

Over the last decade, a slew of charging standards has emerged—the USB-Power Delivery (PD) standard or Qualcomm’s Quick Charge, for instance. A few companies have opted to design their own proprietary standards, such as Oppo’s VOOC fast charging, Xiaomi’s HyperCharge or Vivo’s FlashCharge. Each of these handle the charging via specifically calibrated phone ports and charger controller chips to work at maximum capacity, which is why most fast charging solutions require you to use the bundled charger to eke the most out of the charging process.

Tushar Kanwar, a tech columnist and commentator, tweets @2shar.

Also read: Why we continue to love foldable phones

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