Does a Full Battery Weigh More?

You may be wondering if batteries get heavier when charged fully or if it loses some mass as it discharges. The weight only matters when it comes to calculations or the battery’s chemistry, which is not much of a concern for you as a user.

While the battery charges, the chemical composition changes, which can slightly alter the mass, but not significantly. When the battery discharges, it is equally likely to lose mass.

How To Tell If Your Battery Is Fully Charged

Since you cannot tell the state of charge of a battery by weight difference, the way to know that your battery is fully charged is by an indicator light on the charger. Most have red as the signal for when it is not yet full and green for a fully charged battery. Some chargers automatically stop the charge once it is full.

Chargers have different qualities and slightly differ in how they charge the batteries. The crudest types of chargers use a constant level of voltage and current throughout the charging process.

Higher quality chargers use the ‘trickle charge’ method. Trickle charge is a slow, gentle way of charging the batteries for much longer. 

In the case of a car battery, determining the state of charge involves using a voltmeter or multimeter to measure. First, you must ensure the car engine is off, including the attached electrical appliances.

Then release the latch on the hood to access the battery. If your voltmeter has alterable voltage switches, put it at 12 volts, then attach the clips to the corresponding terminals of the battery.

The positive clip to the positive terminal first, followed by the negative clip. Use the probes to touch the corresponding terminals on the battery, using the negative probe on the negative terminal first, then the positive probe on the positive terminal.

If using a multimeter, set it to read direct current voltage and turn the dial to 20 volts. 

Observe the reading on either of the devices (voltmeter or multimeter); if the reading is at least 12.6 volts, it is fully charged. Anything lower than 12.6 volts indicates that you need to charge the battery. If charged and yet does not increase in voltage, the battery is old or damaged, and you most likely need to replace it. 

What Makes A Battery Weigh More?


The average lead car battery is about 40lbs. Lead is a heavy element that weighs more than 11 grams per cubic centimeter. Also, car batteries are heavier than most because of the electrolyte’s lead content.

Car batteries are surely much bigger because of what they contain, unlike AA batteries with less content that are small enough to fit into your drawer or purse. The lead, casing, electrolytes, and terminals contribute to the significant weight, not how charged the battery is.


The size of the battery tallies with what it powers. A smartphone battery is wider and denser than a remote control battery; therefore, it will weigh more. Likewise, a car battery is bigger, wider, and more packed than a smartphone or remote control battery. 

State Of Charge

A full car battery weighs about 40 pounds, but if the fluid (acid water-electrolyte) depletes completely, the weight can drop as low as 15 pounds. However, charging does not significantly alter the mass of the battery.

Other types of batteries do not lose significant weight when discharged. Charging means that the molecules move from one point to another due to increased energy, and the energy does not translate to tangible mass. The change is infinitesimal. 

Battery Type 

There are different battery types according to their chemical composition. An instance is lead-acid batteries being heavier than Li-ion batteries due to their chemistry. Also, most batteries have steel or aluminum casing, contributing to weight.

Steel weighs five times more than plastic, and aluminum is double the weight of plastic. Plastic battery casings were not commonly used due to relatively low heat resistance.

However, new technology from the Japanese has created plastic casing that is as heat resistant as metals. 

a single car battery

What Does The Weight Of A Battery Affect? 

A battery’s weight matters because it can serve as an indicator of its performance. The weight of your battery should be compatible with your car, not too heavy or too light. Using a big or heavy battery might be unnecessary if your car has a small engine.

Also, if your battery is too lightweight for your engine, it might not deliver the power to run the car properly. 

Battery energy density is another important weight-related factor. Battery energy density is a battery’s energy level compared to its weight or size. It is called specific energy density in relation to size and volumetric energy density in relation to size.

It is measured mathematically by dividing the watt-hours by the weight/volume. The energy density is how long a battery can power an appliance compared to its weight or size. The higher the energy density, the more time the battery effuses charge in relation to the size. Batteries with high energy density are useful for devices that require a lot of energy but small battery space. The battery type with the highest energy density is the lithium-ion battery.  


Can Overcharged Batteries Explode? 

Overcharging batteries can cause the hydrogen and oxygen levels to rise excessively, causing ignition and, in turn, an explosion. Overcharging can also cause the rate of grid corrosion breakdown of the internal battery plate separators to increase, causing short-circuiting and a possible explosion. 

How Long Should It Take To Charge A Battery Fully? 

The time it takes for a battery to reach a full charge depends on the charge amps. It also depends on the type of chargers used.

A trickle charger gets the battery full in more time due to the slow, gentle charging. In contrast, a standard charger maintains a steady current and charges the battery to a full state in a shorter time.

A 20 amp charger will charge a car battery in 2 to 4 hours, while a 2 amp charger will charge the same battery to full state in 12 to 24 hours. 

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