Electronic devices such as smartphones, laptops, tablets, etc. have large capacity batteries that can store significant amount of energy. A number of experiment videos are available online, which reveal how these batteries tend to explode when mishandled. It makes us wonder if all the energy stored in a fully charged battery has some weight to it. In that case, wouldn’t your smartphone weigh more when it is fully charged as compared to when its discharged or running low on battery? Well, to answer such questions, we first need to understand the basics of battery technology.
A rearrangement of ions
Most smartphones have lithium-ion batteries that store energy electrochemically. The primary components include an anode, cathode, negative and positive terminals and electrolyte. It’s essentially a closed structure that utilizes flow of electrons to generate electrical power. When in use, a lithium-ion battery sends lithium ions towards the cathode. This creates a flow of electrons, which in turn powers our devices.
When plugged in, the charging voltage is higher than the battery voltage. This reverses the flow of lithium ions, which start moving from the cathode towards the anode. When the battery is fully charged, most of the lithium ions would have collected at the anode. This cycle keeps repeating throughout the workable life of the rechargeable lithium-ion battery.
No increase in mass
As is evident from the above, the working of a rechargeable battery only involves the flow of ions from anode to cathode and vice-versa. Nothing is being stored inside the battery that may increase its mass. Even if there is difference of some electrons, the change in mass would be unfathomably low and nearly impossible to detect. Based on this, it can be said that batteries do not weigh more when fully charged.
For easy understanding, rechargeable batteries can be compared with wind-up toys. These store energy mechanically when you twist the keys. Inside, wind-up toys have coiled spring system that stores energy. Here too, there is no increase in the weight of the toy after you have twisted the keys to its full capacity. Something similar happens with rechargeable batteries.
Even though charging and recharging do not increase or decrease weight of the battery, other factors can come into play. For example, if there are minute leaks in the battery, it can lose some mass over a period of time. Similarly, factors like humidity can also trigger a change in the battery’s weight. However, these changes too will be pretty miniscule.
Moral of the story is that a fully charged battery does not weigh more. At least not by amounts that can be measured with existing techniques.