When it comes to battery life and maintenance everyone wants to know, what are the best practices to optimise the usage of your laptop battery? The technology and hardware that are used in today’s laptops need more power and the battery requirements have increased. Advancements in batteries have also improved and can last far longer than the few hours you are used to with older laptops. While in the past it was unwise and even dangerous to leave your laptop plugged into an external power source all the time, in new laptops with newer battery technologies this is no longer an issue. There’s no way to “overcharge” these batteries. When your battery gets to 100% charge and you leave your laptop plugged in, the charger will stop charging the battery. The laptop will just run directly off the power cable. After the battery discharges a bit, the charger will kick into gear again and top the battery off. There’s no risk of damaging the battery by charging it over its capacity. In this article, we will explain in more detail why there are no issues when you leave your laptop plugged in all the time.
It’s important to understand the basics of how the standard batteries in modern devices work. There are two main types of batteries used in laptops: lithium-ion and lithium-polymer. Although they are different technologies they function in broadly the same way, generating power through the movement of electrons.
For both types of batteries, the following statements are true (at least as far as modern laptops are concerned):
- A battery cannot be overcharged. There’s no danger of overcharging a battery if you leave it plugged in all the time. As soon as it hits 100 per cent it will cease charging and won’t start again until the voltage falls below a certain level.
- Fully discharging a battery will damage it. Allowing the battery to become completely empty for an extended period can put it into a deep discharge state. This can be fatal—you might never be able to charge it again. (You can try these methods to jump-start a dead laptop battery.)
So, based on this, do we conclude that you should leave your laptop plugged in all the time? Not quite.
The real reasons why all batteries wear down over time
Your laptop battery will always wear down over time. The truth about lithium-based batteries is that they are inherently unstable. They begin to lose capacity from the moment they are produced, and there are numerous factors that hasten their decline. These include:
- Fully discharging – If you let your laptop fully discharge for an extended period of time then it can cause permanent damage.
- Charge/discharge cycles. Every battery has a finite number of times it can be charged and discharged.
- Voltage level. The higher the charge level (measured in volts per cell), the shorter the battery’s life.
- High temperature, over 30 degrees celsius. This can cause irreparable damage.
If you let your laptop fully discharge for an extended period of time then it can cause permanent damage to the battery, and it might never be able to hold a charge again.
To put the definition of full discharge in more technical terms. It is when the battery runs out of power to the point where the chemical process in the battery cannot be fully reversed by charging, effectively rendering your laptop battery useless.
Charge/Discharge Cycle & Voltage Levels
A charge or discharge cycle can be defined as “the process of charging a rechargeable battery and discharging it as required into a load”. The more charge cycles you put the battery through, the more it will wear down. Different batteries have different ratings, but you can often expect about 500 full charge cycles.
This number is usually used to define how long a battery is going to last. When lithium-ion batteries, the most common laptop batteries are charged to 100% capacity they possess 4.2 volts per cell with an estimated 300-500 charge cycle lifespan.
So think of it like this, when your battery is nearly fully charged it has more voltage per cell, but as you use the laptop and the battery percentage decreases. The volts per cell will also gradually decrease.
For every 0.1 Volts drop below the maximum 4.2 Volts per cell that lithium-ion supports you can nearly double the charge cycle.
If you only charge your battery to around 80% your battery can withstand 600-1000 charge cycles as compared to just 300-500 if you kept it at 100% all the time. This is why you often hear people telling you to only charge your electronics to 80% battery capacity.
So if you left your laptop plugged in and charging all the time, it would significantly reduce the number of charge cycles the battery can support. You could start seeing battery degradation before the laptop is even a year old. In saying that if you use your laptop on battery often then you will be using one of the charge cycles. If you plan on using your laptop plugged in then it is better just to leave it plugged in. If you often use it on battery then letting it only charge to 80% can help in the life of the battery
Excess heat will damage a battery over time and reduce its lifetime significantly. Excess heat is typical when you are multitasking and have many programs open simultaneously. High temperatures, typically classified as being over 30 degrees Celsius, will shorten the life of a battery irrespective of any other factors. Simply leaving your laptop in your car on a summer afternoon is a bad idea. When you combine the stress of high temperature with the stress of high voltage, the effects are even worse.
But Should I Leave It Plugged In or Not?
Though the technology has improved significantly in recent years, the death of your laptop battery is still inevitable. The moment you power up your new computer for the first time, the lithium inside starts to degrade. Ultimately, it’s not clear which is worse for a battery. Leaving the battery at 100% capacity will decrease its lifespan, but running it through repeated discharge and recharge cycles will also decrease its lifespan. Basically, whatever you do, your battery will wear down and lose capacity. That’s just how batteries work. The real question is what makes it die more slowly.