# Use and charge a Lithium battery at the same time

I have read this question and its answers : How a battery is being charged and used as the same time?

Question 1 : I would like to know if the same concept can be applied to Lithium battery.
Question 2 : Let's say that the battery is being used, I plug the charger, what happens at this special moment, electrically speaking ?

My use case is this : I built a portable speakers box, a Lithim battery is inside (24V and 18Ah). I have a charger that delivers 24V and 5A. The little amplifier inside can use up to 5A. I want to know if there is no risk from plugging ang unplugging the charger when the music plays.

Schematic diagram of my use case :

Constraint 1 : The vuemeter must not work when the system is OFF.
Constraint 2 : The charger must charge the battery when the system is ON and OFF.
Constraint 3 : The charger must provide the charge to system when it is plugged, instead of discharging the battery.

• you cannot charge a battery and discharge it at the same time Jan 27 '21 at 22:26
• @jsotola : Yeah, this I have read it, but a good explanation of my question 2 would be great for me to understand, thanks.. Jan 28 '21 at 8:00
• Please show a schematic diagram of your setup. If you are charging a lithium battery directly from a 24 V battery without a battery management system then you are at severe risk of fire or explosion. Jan 28 '21 at 8:33
• @Transistor : I am charging the battery with a charger. Let me make a diagram sure. Jan 28 '21 at 8:35
• As explained in my answer that you linked the word "charger" is often used when it is in fact just a constant-voltage power supply. To prevent confusion give the make and model and link to the datasheet of the "charger". Jan 28 '21 at 8:37

What happens is pretty much governed by Kirchhoff's current law. Consider the point at the switch, where the wires from the charger, the battery and the load all meet.

Kirchhoff's law states that the total current going into that point must always equal the total current going out. It's common sense, really - if the law weren't true then electrons would be piling up somewhere.

So if the charger is producing more power than the load needs, then the excess goes into the battery. If not, then the battery will power the load.

If you're not using a proper charge controller, make sure you use a "protected" LiIon battery. Or get a good fire extinguisher.

• Goog explanation thanks ! I am using the kind of charger that is provided with the battery, I bought this one : fr.aliexpress.com/item/1005001465847963.html But I bought another one up to 5A, but it is the same kind... I mean... it is supposed to work together, they are sold together... Are these chargers good ? Jan 28 '21 at 19:31
• The description of the product says (I translated from italian to english) : Inside with protection circuit: over charge, over discharge, over current, short circuit protection Jan 29 '21 at 8:26

There are "power path" charging ICs that manage the adapter current so that the end equipment can be used, and what's left over can charge the battery.

Typically running the end equipment is given priority so the charging rate may be reduced while the equipment is on. It also manages plug in and out events so that the system voltage remains within specified limits.

It works fine with lithium batteries, that's exactly how your cell phone charges while you're talking on it.

Here is an article describing power path management.

Here is an example datasheet of a Li-ion charger with power path management.

• Thanks for this clairification, but how, electrically speaking, the current prefers to starts from the charger and goes back to it, instead of the battery ? In other words, how the charger can say : "I am the charger, you are the battery, don't provide current, I will". Why the charger, when plugged, decides that it is the source of current ? Jan 28 '21 at 7:59
• I ask this because I do not use such device you mention above, my installation is simple, there is no "intelligent device" that decides where the current should go.. Jan 28 '21 at 8:07