What happens if a battery is not charged for a long time?

Have you ever wondered what will happen if you use a battery that has not been charged for years? This question came to mind when I got an old smartphone while searching for other stuff. I got curious and tried to turn it on, but the phone battery was out of juice, so I used a charger to charge it. Luckily, the phone turned on in 15-20 minutes, and now I can use it. You can see the image of the phone below. The screen is broken, but it is working.

phone battery

If you have an old phone or a smartphone and want to keep it with you, the first question about the batteries may come to your mind. Batteries are the first product that gets easily damaged in any electric device.

I will discuss all these things in this post, but let’s see first what happens if a battery is not charged for a long time.

If a battery is kept ideal for a long period of time, it will self-discharge on its own. The self-discharge rate is between 2%-3% per month or more, depending on the quality of the battery. This happens due to internal reactions inside the battery. Once a battery is dead, it cannot be revived back.

However, a method has been developed by the US Department of Energy’s SLAC National Accelerator Laboratory and Stanford University. In this method, the battery degradation slows, and capacity is restored. For full information, you can read this article at Imeche.

How much time does it take to self-discharge a battery?

Typical self discharge rates for a Lithium Ion battery
Image from: research gate “Typical self-discharge rates for a Lithium Ion battery.” By A K M Obaydullah

In my observation, a used battery can fully discharge in 4-6 months from 0-100%. But the discharge percentage is very low for the new one, between 0.5%-2% per month. For better understanding, I have created a table so that It will be easy for you to understand.

TimeBattery percentage self-discharge from 100% – 0%
1 month87%
3 months45%
6 months12%
12 months0%
The battery is kept in a cool place, and it is not more than 6 months old

How long do batteries last when charged for the first time after a long interval?

You may have observed that the battery percentage is between 45% – 65% when you buy a smartphone. Do you know why this happens?

When companies assemble the smartphone, the battery is charged only up to 80%. This is done because if the battery is charged fully to 100%, the rate of discharging will also increase because of a rise in temperature or heat. That’s why it is told by experts to charge our phones between 30%-80% to get a longer battery life.

You can set up an experiment at home using two smartphones. Charge one phone full to 100% and charge your other phone to 80% and let them discharge completly on their own you will observe that the fully charged phone will discharge much faster than the other one. However, this experiment is quite long, and there are a lot of factors that you need to keep in your mind.

How can we detect if batteries are good or in working condition?

To detect whether the batteries you have kept are fine or they are in working condition, here are some tips that you can follow:

Check if batteries are charging

If batteries are not charging or take too long to hold 1%-10% of the charge, they have been fully damaged and can’t be used in any device. This happens when you use a battery for a long time and keep it ideal without charging it occasionally.

Check the discharging rate.

Suppose the discharge rate of the battery is quick. Suppose you charge your battries after a long time, and it charges normally. But the discharge rate is quick such as in 10-15 minutes, the battery discharges from 95% – 70% then it is a sign that the batteries are damaged.

Check if the batteries are swollen.

It is quite easy to figure out if the battries are swollen. The main reason for this swelling in the batteries is an incomplete reaction inside, resulting in hydrogen fluoride gas formation. If you have these types of battries, dispose of them properly.