Have you ever changed the batteries of a TV remote and noticed how light it seems?
Batteries are heavier when charged because of the ions inside of them. Ions absorb energy until they reach their maximum capacity or highest energy state. All of the absorbed energy stockpiles add to the battery’s overall weight. Converting the stockpiled energy to electrical energy will make the battery lighter until all the energy is used.
Example of charged vs uncharged battery weights.
| Battery | Charged Weight | Uncharged Weight |
|---|---|---|
| A | 50g | 45g |
| B | 75g | 70g |
| C | 100g | 95g |
| D | 120g | 100g |
Why Do Batteries Become Heavier When Charged?
Batteries change weight due to the energy state of the ions inside them.
Ions (electrically charged atoms) make it possible for batteries to store and release electrical energy. When you charge batteries, the ions absorb electrical energy and become excited. Excited ions are ions that reach higher energy states. By lowering that energy state back to ground level, the ions release the excess energy in electrical energy.
We talked about how ions change from ground level to high energy states and vice versa, but what does it have to do with the weight of your batteries?
We can think of ions as a piggy bank. By itself, the piggy bank doesn’t weigh much, but putting coins inside causes it to become heavier. Eventually, you’ll reach the maximum number of coins that fit inside the piggy bank. You’ll need to remove the coins inside of it, making the piggy bank lighter, before you can store more.
Increasing the energy state of an ion is the same as putting coins inside a piggy bank. Ions become excited by absorbing energy until they hit the highest possible energy state or, in other words, become fully charged. Using the batteries causes all its stored energy to be released as electrical energy until it reaches ground level and becomes empty.
How Much Heavier is Charged Batteries from Empty Ones?
The difference in weight between a charged and empty battery is very minimal.
Let’s return to the piggy bank example we used before. You typically won’t feel the piggy bank get heavier if you only place a few coins inside, but it will get noticeably heavier once it is full. By nature, the ions inside the batteries are incredibly light and small, so multiplying their weight won’t make a big impact.
The amount of weight a charged battery increases depends on the material it’s made from.
Take your usual lithium-ion or Li-ion batteries; the only time you’ll notice the weight change is when you have both its charged and empty versions at hand- like when you’re in the middle of changing the batteries of a TV remote.
Meanwhile, you’ll immediately notice how much heavier a charged car battery is compared to an empty one. Car batteries are made from lead ion, which is significantly heavier than lithium. However, the overall weight difference between a charged and empty car battery is minimal.
References
How a battery works – Australian Academy of Science. www.science.org.au/curious/technology-future/batteries
Atomic Structure – New Mexico State University. www.astronomy.nmsu.edu/geas/lectures/lecture18/slide02.html
Video References
Basics Explained, H3Vtux
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