New Smartphone Battery Secrets 101 Want maximum run time from your phone battery? There’s more to it than dimming your screen. delves into the science of maximising mobile battery life.
Darren Yates
It’d be fair to say most of us don’t consider the batteries powering our portable devices until they run out of charge. Just like a power supply unit in a desktop computer, phone batteries are indispensable – yet the chances are when it comes to the components inside a phone, the one we least understand is the battery. We’ve all heard the ‘hot tips’ on maximising device battery life from ‘dim the screen’ to ‘turn off GPS’. However, there are other factors that can have far greater effect. This month, we dive into battery science to squeeze more power out of your device battery – and give it longer life.
LI-ION OR LI-POLYMER?
The goal of longer battery life really is a science – and it starts with battery construction. With most phones now featuring non-removable batteries, understanding even just the basics will help you maximise its lifespan. When it comes to phones, you’ll find two common classes of Lithium-based rechargeable battery – Lithium-ion (Li-ion) and Lithium-Polymer (LiPo). The difference? Not much, as it turns out. Keeping it short, a battery has an anode (-), a cathode (+) and a substance called an ‘electrolyte’ to facilitate electron flow. There are many different Li-based battery types depending on the chemical compounds used to create the anode and cathode electrodes. For example, the new Panasonic 18650 cells inside Tesla cars use a cheaper and more effective Nickel-Manganese-Cobalt (NMC) cathode. However, the practical differences between Li-ion and LiPo batteries in phones are more to do with construction. Here, the ‘polymer’ generally refers to the cell packaging, allowing a higher energy density per unit volume.
NOT TOO COLD, NOT TOO HOT
You don’t have to read too many ‘my phone won’t charge’ stories on the web to know Lithium-based batteries are, shall we say, particular about their conditions. For starters, they don’t like heat – and by ‘heat’, we mean anything much over 30-degreesC. Prolonged exposure to temperatures above this level not only reduces the charge capacity, but also reduces the battery’s lifespan. That means you’ll need to recharge it sooner, but also you won’t get as many charge-discharge cycles before it goes belly-up.
This has ramifications for high-demand applications, particularly gaming. Playing high-performance games requiring plenty of processing power raises the temperature of the CPU and GPU cores inside your phone’s processor chip. Given the proximity of the battery to the main circuit board and chip in most phones, a rise in battery temperature is almost unavoidable.
Yet Lithium-based batteries don’t like being too cold, either. Australian Research published last year by RMIT University showed Li-ion batteries can lose as much as 23% of their capacity when operated at -15degreesC ( tinyurl.com/y7pdmqhd). Not only that, but colder batteries take longer to charge. The internal chemistry of the battery cell changes at lower temperatures, increasing its internal resistance, which reduces the amount of charge current they can accept, pushing out charge times. Sure, most of us don’t live at -15degreesC, but it’s a progressive thing – the colder the battery, the lower its capacity becomes (it’s also an issue for electric cars).
So what’s the ideal temperature? It turns
out the sweet-spot is about 20-degreesC – that gives you the maximum capacity as well as longest life-span. Much either side of that mark and you start to lose either way.
OVER-CHARGING
Another thing Lithium-based batteries don’t like is being over-charged – and this can mean charged too fast as well as charged for too long. All phone batteries have protection circuitry built in that automatically prevent this from occurring, but there’s still debate over what constitutes ‘too much charge’. Phone makers obviously want a safe battery, but they also want to pack in enough energy to ensure decent battery life. A smartphone battery features a single cell with a nominal cell voltage of 3.6 or 3.7-volts. When you plug in your phone charger, it pumps electrical current into the cell, which progressively raises its voltage. Once it reaches 4.20-volts, the charge current is cut and you’ve reached full-capacity. However, there’s argument that 4.20-volts is too high, that it causes battery stress and that stopping a charge at 4.05-volts is better in the longer term. You’ll find apps on Google Play like AccuBattery ( tinyurl. com/y7x55tsh) similarly advocating you unplug your phone once its charge level reaches 80%, rather than letting it hit the 100% end-stops. In fact, according to Battery University ( tinyurl.com/ ybx6862q), for each 0.1-volt below 4.2-volts you drop the peak charge voltage, you double the charge cycle lifespan. That means while charging to 4.20-volts will get you 300-500 charge cycles, charging to only 4.10-volts will bump that to 600-1000 cycles. Of course, a battery charged to 80% requires charging sooner, but should pay you back in the long run.
However, it’s not quite that simple. Recent developments have seen new Lithium-NMC batteries with nominal voltages as high as 3.8 and 3.85-volts. The higher voltage helps boost capacity and potentially allows a maximum charge voltage of 4.35-volts and 4.40-volts, respectively. So, battery chemistry determines the appropriate peak charge voltage, something phone makers take into account during their design phase.
Still, my Motorola Moto G5 with its 3.8-volt LiPo battery was shown by two apps – AccuBattery and Ampere – to be charging at 4.39-volts at a charge level of 91%. Does this constitute over-charging based on the arguments? You couldn’t say for certain. Still, given the data available, I’m less inclined to go past a 90% charge level in future.
However, there is one thing everyone agrees on – you definitely don’t want a 100% fully-charged battery exposed to excessive heat. That’ll kill it as fast as anything else. NO FULL CHARGE-DISCHARGE CYCLES This also flows into that old chestnut of an idea that you must fully discharge and then fully charge your phone to get maximum battery life. It may have had some truth to it in the days of NickelMetal-Hydride (NiMH) batteries, but these full charge-discharge cycles do Lithium-ion batteries no favours. For a typical Li-ion cell, you’ll get roughly 300 full-depth discharge cycles, but if you reduce the ‘depth of discharge’ to just 40%, you’ll get around 1,000 cycles. Put all together, keeping your phone battery’s charge level between 40% and 80% should be your best bet for achieving maximum life-span.
If you’re up for it, a 2016 IEEE research paper from MIT and ETH Zurich called ‘Modelling of lithium-ion battery degradation for cell life assessment’ ( tinyurl.com/ycomuzne) tests various charge level ranges and explains how it all works. IS FAST-CHARGING SAFE? Bigger phones have bigger screens, bigger screens need bigger batteries, bigger batteries need faster charge rates. Pretty much all phone chargers will slam a battery at a low-charge state with maximum allowable electrical current to pump the power in as fast as possible. However, once that rate reaches around 80%, the current rate is progressively reduced to protect the battery.
Your phone may have come with, or have an option for, a fast-charger that speeds up the charging process and reducing charge times, but there are two things to remember about this. First, fast-charging generally causes greater stress to the battery, including raising its temperature. The second thing is that fast-charging works best with batteries at a low-charge-state. Once a battery reaches a charge level of around 80%, fast-chargers are generally little better than standard ones, because essentially, it’s the battery now controlling the charge rate to prevent damage to itself.
WHAT ABOUT WIRELESS CHARGERS?
Wireless chargers might seem convenient, but they also can have the added issue of generating extra heat. Inductive charging works by having two wire coils in close proximity. Energy pumped into the transmitting coil is picked up by or ‘induced’ in the receiving coil. The problem is that like all energy transfer systems, you don’t get 100% efficiency, which means some energy is lost as heat. Given that the receiving coil is often close to the battery, that energy loss can result in increased battery temperature.
COST VS CONVENIENCE
If you’re the type to replace your phone every two years like clockwork, you probably won’t care how warn out the battery might be. But with plenty of top-end phones now pushing well north of $1,000, non-removable batteries are hardly cause for celebration.
Some argue that it’s only $80 or so to send your phone back to wherever for a battery replacement, but that raises privacy and security concerns. A user-removable battery overcomes this problem.
BE SMART
Smartphone batteries have built-in protection smarts already, but you can help your phone battery last longer by following these five tips: Don’t allow the phone temperature to fall below 10-degrees C or go above 30-degreesC for extended periods (and definitely don’t leave it in the car). Aim to maintain a phone charge level range of between 40 and 80% (yep, you’re reducing the capacity and run-time but it reduces battery stress longer-term). Don’t fully discharge your phone before charging it (the battery lifespan will be longer with ‘partial’ charges rather than full ones). Definitely don’t fully-charge the battery and expose it to high temperatures. Grab a good battery monitoring app like AccuBattery. So, in short, a fully-charged battery is bad; a fully-charged battery that’s hot is worse. No matter how great your phone is, it won’t work if the battery’s shot. Lithium-based batteries are fussy and you’ll likely lose some lifespan if you don’t look after it.