For over a decade, solar panels have been appearing on roofs all around us, converting ordinary sunlight into clean, green energy. At the same time, electric cars have become a common sight on the streets. You might think it all goes without saying, but the physics behind batteries can be quite confusing – even experts make mistakes sometimes. Below, you’ll find information to help you better understand datasheets and the differences between battery types.
What is voltage (V)?
Voltage is the difference in electrical potential between two points. If you compare electricity to water, voltage is like the pressure in a garden hose. Even a small amount of water can have a big effect if the pressure is high enough – think of a pressure washer.
A voltage of up to 50 volts is considered safe for humans in most situations. At higher voltages, safety precautions must be taken (see the section “safety”). Battery cells usually have a voltage range between 2,5 V and 4,2 V. If you want to achieve a higher voltage, you connect several cells in series: 10 cells of 3,6 V together deliver 36 V.
An important characteristic of batteries is that the voltage drops as the charge decreases. A fully charged lithium-ion cell has 4,2V, while when almost empty it can drop to 2,5V. For this reason, the cell is often noted as 3,6V – the average between full and empty. Note that the voltage at the end of the charge cycle is higher, which is important when designing systems and choosing the right components. For example, a battery pack with a nominal voltage of 360V can increase to 420V when fully charged.
What is current (A)?
Current is the amount of electrical charge flowing past a point per second – also known as amperage. Using the water analogy again, current is the amount of water flowing through a pipe per second. Even at low speed, a large volume of water can have a big impact, like the waves at sea.
Although high current at low voltage is usually not directly dangerous, the consequences can still be serious. For example, current peaks can lead to considerable heat development, which in turn can cause burns. (See also the section “safety”.)
Battery cells come in all sizes. The familiar 18650 cells often used in laptops can deliver a few amps. Large prismatic cells, on the other hand, can deliver hundreds of amps. By connecting multiple batteries in parallel, you can increase the total current (A) of a battery pack.
What is a battery?
A battery is an electrochemical cell with two external terminals, which supplies electrical devices with electricity. The negative terminal is the source of electrons, which flow to the positive terminal via an electrical device. While the electrons, for example, light a lamp, chemical processes take place inside the battery.
Ions are released from the negative electrode (anode) and move via the electrolyte to the positive electrode (cathode), where they are absorbed. The flow of electrons stops as soon as all the active material in the anode and cathode has been converted: the battery is then empty. When charging – provided the battery is made of rechargeable materials – this process is reversed.
Batteries were used in electric vehicles as early as the late 19th century. Thomas Edison had one, for example. In the early 20th century, 38%(!) of cars in the US were electric.
Edison said about this:
“Electricity is the future. No rattling and grinding gears with countless levers that confuse, no dangerous and smelly petrol, and no noise.”
What is capacity (Ah or mAh: 1Ah = 1000mAh)?
Capacity is the amount of current a battery can deliver over a certain period of time, usually expressed over one hour. For larger batteries this is usually stated in Ah (ampere-hours), for smaller cells often in mAh (milliampere-hours).
For example, a battery labeled “2500mAh” can deliver 2,5 amps for one hour. This ratio can be adjusted: the same battery can also deliver 1,25A for 2 hours, or 5A for 30 minutes.
There are both low and high capacity batteries, ranging from 1500mAh (like standard 18650 cells) up to 300Ah (300.000mAh) or more. In practice, that maximum capacity is often only achieved at a low current draw, usually around 20% of the specified value. In this example, that means the battery can deliver 0,5A for 5 hours.
If you use a higher current draw, heat is generated in the battery and energy is lost — the specified capacity is not fully achieved. The smaller this loss, the better the battery is suited for applications with a high load (high drain).
Sometimes suppliers only give the capacity of the battery. If you know the voltage, you can calculate how much energy the battery contains. If the voltage is unknown, for example in composite battery packs, then you miss a crucial factor to estimate the total amount of energy.
What is the C-rate?
The C-rate (or C-value) indicates how quickly a battery can be charged and/or discharged, and is strongly related to the capacity of the battery. Note: the “C” does not stand for “capacity”!
This C-value is useful for comparing the (dis)charge current of batteries of different sizes.
The capacity of a battery is usually specified at 1C: a fully charged 2500mAh battery should then be able to deliver 2,5A for 1 hour.
You can use the C-rate to determine the relationship between (dis)charging current and time. For example: a 2500mAh cell with a discharge C-rate of 3C can be discharged with 7,5A (because 3 × 2,5A).
If the current is 3 times as high, the usage time is theoretically 3 times shorter. So in this case the battery can theoretically deliver 20A for 7,5 minutes. In practice this will be a bit shorter due to losses such as heat development and voltage drop.
What is power (W or kW: 1kW = 1.000W)?
Electrical power, like mechanical power, is the amount of work done. It is calculated by voltage to multiply by current (Current).
For example: if your battery pack can deliver 500A at 400V, then it delivers:
500A × 400V = 20.000W or 20kW.
This is the information you need to determine whether your battery pack can deliver enough power for your application.
Please note: some battery suppliers only list the absolute maximum power that their pack can deliver. Often this is only a few seconds long, and sometimes even exceeds the design limits of the cells used.
So: read the fine print carefully and ask questions. You should always check whether the battery pack can actually deliver the specified power for the required time.
What is energy (Wh or kWh: 1kWh = 1.000Wh)?
There are different definitions of energy, depending on the field. Here we limit ourselves to the following:
energy is the amount of power (W or kW) delivered during one hour.
If this is not specified by a supplier, you can easily calculate it yourself by multiply the capacity of the battery pack by the voltage.
For example: a 500Ah battery pack with a nominal voltage of 400V is a 20kWh pack.
Please note that you must nominal voltage used and not the maximum voltage.
This is very important information because it determines the size of your battery pack, price en what you can do with it.
If the aforementioned 20kW battery pack can only deliver this power for 5 minutes, it contains much less energy than a battery pack that can deliver 20kW for five hours.
The amount of energy a battery pack can store is often referred to as the “battery size” of “battery capacity”.
Strictly speaking, that is not entirely correct, because those terms are not actually expressed in the correct units of energy.
Especially the term “battery capacity” is confusing: capacity is important, but only in combination with the tension you can determine how much energy a battery pack can actually store.
What is energy density (Wh/kg or Wh/l)?
Especially in mobile applications it is often important that a battery pack is as light and compact is possible, and yet as much energy as possible contains.
More energy means that you can use a certain amount of power for longer, which in a vehicle, for example, means more range.
When comparing different cells and batteries you can calculate the amount of energy in relation to weight (gravimetric) and the size (volumetric).
For example:
A 24kWh Nissan Leaf battery pack weighs 294 kg and has a volume of 494 liter.
- Gravimetric energy density: 24.000Wh / 294kg = 81 Wh / kg
- Volumetric energy density: 24.000Wh / 494L = 48 Wh / L
That's pretty low.
For example, our own 72 Volt “range” battery pack has these specifications:
- Gravimetric energy density: 190 Wh / kg
- Volumetric energy density: 316 Wh / L
You can also calculate it the other way around:
If we were to fill 494 liters with our batteries, we would get:
494L × 316Wh/L = 156.104Wh or 156kWh of energy.
That corresponds to six Nissan Leaf battery packs.
Please note: we are comparing here battery packs, not single cells!
You also have to take into account the mechanical housing en internal subsystems.
Loose cells do have better numbers, but you can't just throw them in your trunk, right? 😉
What is power density (W/kg or W/l)?
Power density is the amount of power you get from a certain mass of scope can get.
Especially with high performance applications With limited space, such as motorcycles or karts, this is an important factor.
Take the Nissan Leaf battery pack as an example again.
Which can 110kW deliver, weighs 294 kg and has a volume of 494 liter.
- Gravimetric power density: 110.000 / 294kg = 374 W / kg
- Volumetric power density: 110.000 / 494L = 222 W/L
That's also quite low.
For example, our 72V “race” battery pack has the following specifications:
- Gravimetric power density: 1850 W / kg
- Volumetric power density: 2830 W/L
We can calculate it the other way around:
If we were to fill 494 liters with our batteries, we would get:
494L × 2830W/L = 1.398.020 W or 1398 kW (1,4 MW) of power,
compared to the 110 kW of the Nissan Leaf.
That is more than 12 times as much power.
So…if you ever have a megawatt sports car want to build: take contact with us! 😎
Please note here again: we are comparing battery packs, not single cells!
Power Density vs Energy Density
Just like in life, you can't have everything at once.
If you go for maximum power, you sacrifice range.
And if you want maximum range, you have to make do with less power.
Do you want both? Then you will have to compensate and compromise.
This might just be the main choice that you need to make when selecting a battery.
The reason is actually very logical:
If you are using a lot of power want to pull out of a cell, the metal poles hot inside.
There is only a limited amount of current that can be passed through a given gauge.
You can solve that by removing those poles to make bigger – but then they take up space
which would otherwise be used for the battery chemistry itself.
And so you lose energy storage capacity.
The same applies conversely:
If you don't need much power, you can optimize the battery for maximum energy,
but then you have to do not overload.
If you do that, then you overload the battery:
- the tension drops considerably,
- a lot of heat is generated,
- and in the best case the battery wears out quickly,
- in the worst case he literally melts through.
Heat generation increases exponentially with current,
so it quickly gets out of hand.
Therefore stay always within the specified current limits
en be on your guard for manufacturers who claim that they can provide maximum power
and deliver maximum energy.
That is physically impossible.
Think of it as a comparison between a weightlifter expats must register with the local municipality and obtain a marathon runner.
Let the weightlifter run the marathon, or the runner lift weights –
both will be bad at it, and the runner will likely get injured.
Just like a range pack gets damaged if you try to pull too much power from it.
Of course you can look for a type decathlete -
someone who can do both fairly well, but will never excel in either one.
Our “performance” battery is comparable to a decathlete.
The graph shows how our solutions relate to power and energy.
Chemical composition of batteries
There are many types of batteries, but we will limit ourselves to lithium batteries here. Why? Because lithium batteries are, now and in the near future, simply the only serious choice for applications where energy density is important. Other chemistries simply do not come close when it comes to performance, weight, or lifespan. Within the lithium family, there are several subtypes (such as LiFePO4 or NMC), each with their own specific properties, but that is fodder for a separate paragraph. For now: lithium is king.
What is State of Charge (SoC)?
The State of Charge, or SoC, indicates how full a battery is. 100% means full, 0% is empty. Sounds simple, but measuring SoC correctly is quite complex. There are roughly two ways in which this is done:
1. Voltage measurement (Voltage method)
An empty battery has a lower voltage than a full one, so you would think: measuring = knowing. Unfortunately, it is not that simple. The voltage does not drop linearly; it drops quickly after 100%, then remains fairly constant for a long time, and plummets back towards 0%. In the range between approximately 80% and 20% it is therefore difficult to estimate the SoC well, especially under load where the voltage drops temporarily. Cheap BMSs (Battery Management Systems) often use this method, which you can see from the somewhat erratic behavior of the SoC indicator.
2. Current integration method
This measures the current consumption (amperes) over time. Because the capacity of the battery is known, you can count down to zero. This method is more accurate, but not perfect. If the load is higher than the system is designed for, the effective capacity drops, and the battery can be 'empty' before the SoC indicates this. Also, the system can drift over time, requiring periodic resetting - usually done automatically after a full charge cycle.
3. Kalman Filtering
To compensate for the shortcomings of both methods, we use advanced software. A Kalman filter combines the data from both systems to a much more accurate estimate of the SoC. This technique comes from signal processing and is widely used in modern systems – such as ours.
What is Depth of Discharge (DoD)?
The Depth of Discharge (DoD) is actually the opposite of SoC. Where SoC indicates how much charge there is still in sits, DoD indicates how many there are consumed is. 0% DoD means a full battery, 100% DoD means fully discharged.
Why is this important? Because batteries are usually not allowed to be discharged to 0% – that is bad for their lifespan. The higher the DoD, the greater the load on the battery. In many applications it is wiser to limit the DoD, for example to 80% or even less, to extend the lifespan. You are then consciously choosing less range, in exchange for longer durability of your system.
Charging the battery
A charger is a device that “pushes” current into a battery to increase its State of Charge (SoC). This sounds simple, but lithium batteries are actually quite sensitive to temperature, voltage, and current. Assuming normal temperature and voltage, the charging process consists of two phases:
Phase 1: Constant Current (CC)
The charger delivers a predetermined current to the battery. How much current depends on the application and what the battery can handle. A safe value for normal charging is for example 0,5C (half capacity per hour). During this phase the voltage slowly increases. Once the maximum voltage per cell is reached – usually 4,2V for lithium-ion – this phase stops. Continuing to charge with constant current would drive the voltage up even further and damage the battery. At this point the battery is about 80% full.
Phase 2: Constant Voltage (CV)
The charger keeps the voltage constant at 4,2V per cell and gradually reduces the current. The current drops to almost zero once the battery is fully charged. Because the current is gradually decreasing, charging the last 20% takes almost as long as charging the first 80%. That is why many electric vehicle manufacturers indicate their charging times up to 80%. During fast charging at the roadside, it is usually practical to charge to 80% and then continue driving.
Together, we call these two phases “CCCV” charging, and this is the only correct way to charge a lithium battery. Other tricks are unnecessary or even harmful. For example, lithium batteries do not suffer from the memory effect that older NiMH batteries had, and trickle charging actually shortens their lifespan. “Conditioning” is also not necessary: lithium batteries are at their best when they are delivered. So only use chargers that work according to the CCCV principle.
We can supply chargers that work perfectly with our batteries and our battery management system (BMS). These chargers are fully programmable and can be adjusted to any situation.
What is also important:
- Do not keep the battery at maximum voltage for a long time, as this will shorten its lifespan.
- Trickle charging is not recommended.
- Fast charging speeds up the first part of the charging process, but the last 30% takes longer. Fast charging is especially useful if you want to get going quickly.
- It is best to plan your charging sessions when the battery is almost empty, as this is when it charges fastest.
Racing and fast charging:
When racing, you want the battery to be completely full for maximum capacity. Even with fast charging, charging the last few percent takes more than an hour. So there is no point in constantly driving with a full battery, because that is extra weight you are carrying around without extra range. Our batteries are fully charged just before the race and immediately returned to storage level after the race to minimize wear.
Temperature and charging:
High temperatures are bad for batteries and can occur during fast charging. That is why our batteries have a liquid cooling system that dissipates the heat well, so that they can be safely charged at the maximum current. In case of overheating, the BMS pauses charging until the battery has cooled down. Lithium batteries can withstand cold quite well, as long as they are not in use. Charging below 0 °C is prohibited, nor is regenerative braking (which also charges the battery). Our BMS can even preheat the battery via the coolant to make this possible in the winter.
Communication between BMS and charger:
The BMS sends instructions to the charger via CAN bus based on battery status, SoC and temperature. This way the charging process is always optimally tuned.
Starting with low power:
Charging starts slowly to protect the battery. Lithium batteries do not suffer from memory effect, so you can charge them at any SoC, fully charge them or just quickly top them up to reach your destination.
“Battery Recovery” Claims:
Some chargers claim to be able to “recover” batteries that the BMS has declared will no longer charge. This is impossible; lithium batteries cannot be regenerated. Sometimes they can boost a battery that has been discharged too far so that it is above the minimum safe voltage and the BMS will allow charging. But often these batteries are already damaged, and even pose a fire hazard.
Storage and maintenance:
Charge your battery regularly, even when not in use. Never leave it below its minimum voltage for long periods of time, as lithium batteries lose charge slowly, even when not in use. Store batteries preferably at around 50% SoC and just below room temperature. Do not store fully charged or empty for long periods of time.
Cell balancing in series:
A battery pack consists of cells in series, and each cell must remain within safe voltage limits. That’s why each cell has a BMS chip that monitors the voltage. Without that control, a single cell can be overcharged or overdischarged, causing serious damage. The weakest cell determines the capacity of the entire pack — just as the weakest link determines the chain.
To balance:
If cells charge unevenly, the BMS can drain excess energy from a full cell (balancing). Our BMS does this automatically during charging, without you having to do anything. With a well-built package, this is not a problem and the capacity remains good. With outdated or incorrectly used packages, balancing takes longer and the capacity decreases.
What is constant current constant voltage (CCCV)?
This is the recognized and correct method to charge a lithium battery, as explained earlier in “battery charging”. First you charge with a constant current and then with a constant voltage.
What is battery balancing?
This is the process of bringing each cell in a battery pack to exactly the same voltage level. For more info, you can go back to the “charging” and “BMS” sections.
What is Electromagnetic Interference (EMI)?
EMI is a disturbance in electrical circuits caused by electromagnetic induction. In an electric car, the biggest sources of this are the motor and the controller, because these devices send and receive powerful and frequently pulsating signals. It is therefore important to keep the cables between the motor and the controller as short as possible, use shielded cable, and place sensitive electronics, such as your BMS module, well away from these components.
What is the CAN bus?
This is a global standard, mainly used in the automotive sector, that allows devices to communicate with each other without a central computer or server. It is fairly resistant to EMI (electromagnetic interference) and is therefore the system of choice in electric vehicles. It is a message-based protocol that is standardized in such a way that many different devices can talk to each other. For example, the charger communicates with the battery management system, which in turn communicates with the battery.
Overview and Coherence of Battery Knowledge for Lithium Batteries
Choosing and using lithium batteries is all about finding the right balance between energy storage, power, security en Lifespan. Below you can see how the different concepts come together:
- Energy density (Wh/kg or Wh/l) determines how much energy a battery can store relative to its weight and volume. This is especially important for applications where weight and space are limited, such as in electric vehicles.
- Power density (W/kg or W/l) is about how much power (or strength) you can get out of that battery in relation to weight and volume. High power density is crucial in applications that require a lot of peak power, for example racing cars.
- Tension between energy and power: You can’t have the best of both worlds — if you optimize your battery for high power (strength), you’re going to sacrifice total energy capacity (and therefore range). And vice versa. This is the single most important compromise in battery design.
- Chemical composition of lithium batteries determines their basic characteristics. Lithium is now the best choice for high energy density and longevity.
- State of Charge (SoC) en Depth of Discharge (DoD) are indicators that tell how full or empty the battery is. Accurately measuring SoC is complex and is improved with smart algorithms like Kalman filtering to be accurate.
- Charging the battery follows the CCCV method (constant current, constant voltage), a standardized and safe way to charge lithium batteries without damaging them. Charging up to 80% is relatively fast, but the last part takes longer to protect the battery.
- Balancing cells is essential because a battery consists of many individual cells. If a cell shows abnormal behavior (more or less charged), this can limit or damage the entire battery. The BMS (Battery Management System) keeps a close eye on this and corrects automatically.
- Safety and durability: Lithium batteries are sensitive to temperature, charging voltage, and charging current. High temperatures and charging at too low temperatures can cause damage. Cooling and heating, controlled by the BMS, ensure that the battery continues to function optimally.
- Electromagnetic Interference (EMI) en CAN bus communication: To prevent interference in the electrical system of vehicles, short and shielded cables are used at motor and controller. The CAN bus ensures robust communication between charger, BMS and battery, even in electromagnetically harsh environments.
Conclusion: Why Power Battery is the Best Choice for Your Energy Needs
At Power Battery, we understand that your battery should be more than just a source of energy. It’s the heart of your electrical system, which is why we deliver nothing less than the very best lithium batteries — carefully engineered to provide the perfect balance of maximum energy, high power, security en long lifespan.
Our batteries are the result of in-depth knowledge of chemistry, advanced technologies and smart software. With our smart BMS systems By monitoring and balancing each cell individually, we guarantee reliable and safe operation, even under the most demanding conditions. Thanks to our unique liquid cooling, our batteries always remain at the optimum temperature, which means they charge faster and last longer.
Power Battery's chargers work according to the proven and safe CCCV protocol and are fully programmable to work seamlessly with our batteries, not only ensuring fast charging times but also protecting your investment from premature wear.
Our technology is built to perform—whether you need maximum range for everyday riding or peak power for intense racing. And with reliable CAN bus communication and extensive protection against electromagnetic interference, you can be sure of a battery that’s always ready to go.
Choose Power Battery and experience the confidence that comes with a battery designed to perform, protect and keep performing — today, tomorrow and for many miles to come.
