That phone in your pocket is a modern miracle. Ditto the laptop on your desk, the tablet in your backpack, maybe even the watch on your wrist. And regardless of what each is capable of, they all have one cornerstone component to thank, one that you probably ought to know how to take care of: A battery.
The first step to knowing your device’s battery is to narrow down the kind. The first kind you might think of (and the kind you probably grew up with) are nickel-metal hydride, or NiMH batteries. These, generally, are the ones that look like a normal disposable batteries, except you can plug them into a wall charger for some extra juice whenever your TV remote dies.
The batteries in your modern-day gadgets—from iPhones to laptops to Bluetooth headphones to tablets—are a different beast entirely. These are lithium-ion (aka li-ion) batteries, and they have some pretty significant advantages over NiMH and other rechargeable batteries that came before. Lithium-ion batteries are also totally different from straight-uplithium batteries,which aren’t rechargeable.
That old saw about how you always need to charge your battery all the way up, and use it until it’s dead? Memory effect, as it’s called, affects NiMH batteries but it doesn’t apply to your phone. In fact, you’re phone’s battery hates when you do that. Similarly, lithium-ion batteries don’t need to be “calibrated” with a full charge and a full discharge when they’re new.
Li-ions can pack a lot of power into a small size, and they don’t lose too much of that energy to leakage when they’re not in use. It’s a combination of these factors that make them great for your portable gadgets.
How does a lithium-ion battery work?All batteries work by having two electrodes—an anode and a cathode—with a bunch of a material called electrolyte between. When you plug a battery into a completed circuit, a chemical reaction starts taking place at the anode and electrons start building up over there . Those electrons want to travel to the cathode, where it’s less crowded, but the electrolyte between these two parts keeps the electrons from taking the short way there. The only way through is the circuit that the battery is crammed into, and those electrons power your device in the process. Meanwhile, the positively charged lithium ions the electrons leave behind travel through the electrolyte to meet the electrons on the cathode side.
Once all the electrons have made the trip, your battery is dead. Except! If you’re using a rechargeable battery like a lithium-ion, you can reverse the process. If you dump energy into a circuit using a charger, you can force the reaction to go in the other direction and get that electron party at the anode all crowded again. Once your battery is recharged, it’ll mostly stay that way until there’s something for it to power again, though all batteries leak some charge over time .
What determines the capacity of the battery—how long it can power your stuff—is the number of lithium ions that can nestle themselves into the tiny, porous craters of the anode or the cathode. Over time, with repeated charge the anode and the cathode degrade, and can’t fit as many ions as they used to. As that happens, the battery stops holding a charge as well as it once did.
How does a lithium-ion battery recharge?
It’s easy to think of charging a battery as though you’re filling a tub with “power.” Just hook up the hose until it’s full! From the outside, that’s exactly how it works, but on the inside it’s a little more nuanced.
A lithium-ion battery typically charges in two stages. First comes the process called constant current charging. This is the part that really is pretty simple. The charger for your phone or tablet will apply a steady current of electricity to the battery to get all those electrons back to the anode. During this stage, the charger just decides how much power is coming out of the firehose and starts spraying. The higher that constant current, the faster the battery can charge. High-voltage quick chargers—like the ones that are starting to come with a lot of new phones—take advantage of this first stage to cram in the juice as quickly as possible (at the cost of a bit of extra stress on the battery).
When the battery is 70 percent recharged, the procedure changes and flips over to constant voltage charging. During this second stage, the charger makes sure that the voltage—that is, the difference in current between the battery and the charger—stays the same rather than keeping the current constant. Practically, this means that as the battery gets closer to full, the current the charger sends into it decreases. As the battery gets full, the rate at which it charges slows down. Once you reach 100 percent, the charge simply trickles in, just enough to account for the tiny, tiny bit of charge your battery loses naturally over time.
So what about over charging? al writer for iFixit, who explained why.
All modern Li-Ion rechargeable devices have some sort of power management IC, designed to prevent overcharging the battery. They’ll keep your phone battery topped off and ready to go throughout the night with a trickle charge at most.
No matter how many times you bring it back to life, your battery will die someday, or at least degrade into a shadow of its former self. That’s unavoidable. Most lithium-ion batteries have a rated lifetime of somewhere between 500 and 1,500 charge cycles .
One cycle is just one bout of discharging, but how much energy you discharge in one go—a measure referred to as depth of discharge (DoD)—matters bigtime. Lithium-ions really hate a deep depth of discharge. According to Battery University, a staggeringly exhaustive resource on the topic, a li-ion that goes through 100 percent DoD (the user runs it down all the way to zero before recharging) can degrade to 70 percent of its original capacity in 300-500 cycles. With a DoD of 25 percent, where the user plugs it in as soon as it gets to 75 percent remain, that same battery could be charged up to 2,500 times before it starts to seriously degrade.
What’s far more dangerous to a battery’s well-being is heat. Lithium-ion batteries despise heat. A li-ion battery that’s been exposed to temperatures of around 100 degrees Fahrenheit for a year will lose about 40 percent of its overall charge capacity. 75 degrees, it’ll lose only about 20 percent.
Something that’s not an issue is overcharging. Contrary to what you might think (or have been told), leaving your phone or laptop plugged in all the time is not bad for its battery. That’s because your gadgets, the batteries in them, and the chargers you attach them to are actually pretty smart about the way they do business.
Trickle charge—what your battery gets when it’s connected and full—is way less distress to the battery’s health than a larger discharge would be.