More threads by David Baxter PhD

David Baxter PhD

Late Founder
What happens when battery is fully charged but still connected?
by AshishMohta,
August 27, 2019

What happens when the battery is fully charged but still connected? The question here depends on the type of battery we are talking about. Since most of the devices now have Lithium-ion and Lithium-polymer batteries, we will take that into context. That said, let us take a step back. Any battery if overcharged will heat up or blow up or lose capacity. However, technology has advanced enough that it can be avoided. In this post, I will share what happens when the battery is fully charged but is still connected. It applies to laptops, mobile phones, and rechargeable batteries.


What happens when the battery is fully charged but still connected?
Many of us put our phones and laptop at charging during night. It makes sure that it’s up for the prime time when you get up. However, many feel worried if it will blow up or overheat as full charge usually takes 2-3 hours tops. Here is the deal. OEM’s have made sure that those batteries are not overcharged even if kept for long.

Protection Circuit
Technically, these days batteries don’t overcharge, thanks for OEM’s implementation of internal protection feature. As soon as the battery hits 100% mark, the internal circuit disconnects the power source from sending any other current. The power circuit is designed to detect the upper limit and will cut off the power connection when it reaches the limit.

So as soon as the battery is ultimately charged, it stops receiving charging energy. The circuit bypasses current directly to the power supply system of the laptop. It breaks one of the laptop battery myths that the battery always powers laptops.

Rechargeable batteries
In the case of rechargeable batteries, it entirely depends on the OEM. While it works on the same principles, check with the OEM if they offer a circuit breaker when the charge is complete.

Most of the mobile phones and laptops come with this feature, but still, make sure to check with your OEM.

Should you keep the laptop plugged in all the time?
There is no straight forward answer to this. Every OEM has its recommendation. Some OEMs are ok if you keep it on charge all the time, while some recommend you to discharge the battery from time to time. It keeps the battery functioning properly.

That said, here is another factor you need to consider. If you live at a place where the temperature is high, it’s a good idea to unplug from time to time, plug it only when the battery percentage falls below a certain percentage. The high temperature usually reduces battery capacity.

Is it better to remove Laptop battery when plugged in?
It’s not a good idea because if the power fails, you will lose your work. However, many follow this pattern thinking it will increase battery life as the use will be less. That said, internal heat is one of the significant factors which impacts battery life.

When using the laptop for casual work which doesn’t heat the computer, keep the battery in the laptop socket. If you are doing intense work, which generates a lot of heat, and for a longer duration, it is best to take it out.

So it’s not just about the ambient temperature but also about internal temperature. A lot of gaming laptops offer a cooling feature which increases fan speed and bent out heat or lower CPU usage, etc. These cooling features can also be turned on manually for some laptops.

How does over-discharging impact battery life?
Just like overcharging, over-discharging is terrible. If you do not charge the battery for a long time, it loses its capacity. Battery develops internal resistance, and the chemicals start depositing. That causes problems.
Replying is not possible. This forum is only available as an archive.