Batteries in Series Parallel
Batteries are one of the most commonly used devices which achieve the desired operating voltage by connecting several cells in series and each cell adds its potential voltage to derive at the total voltage terminal. The connections which are parallel, they attain higher capacity by adding up the total ampere-hour that is Ah.
Some of the packs may also consist of a combination that is of parallel and series connections. Such a configuration is called the 4s2p that means four cells which are in series and two which are in parallel. The foil which is Insulating foil between the cells that prevents the conductive metallic skin from causing a short of electric current.
Most of the batteries that are chemistries lend themselves to parallel and series connections. It is very important to use the battery which is the same type with equal capacity and voltage that is Ah and it is never to mix different makes and sizes. A cell which is weaker would cause an imbalance. If we look at the analogy we can see that a chain in which the links represent the cells of a battery are connected in series
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A cell which is a weak cell may not fail immediately but will get exhausted very quickly than the strong ones when on a load. The low cells in charge fills up before the strong ones, that is because there is very less to fill and it remains in charge over longer than the others. On the discharge the cell which is weak cell empties first and gets hammered by the other cell which is stronger. Cells in multi-packs must be matched especially when it is used under heavy loads.
Single Cell
The configuration of the cells which are single-cell is the simplest battery pack, the cell probably does not need protection and the matching circuit on a small Li-ion cell that can be kept simple.
Typical example are mobile phones and tablets with one 3.60V cell. Other uses of a single cell are wall clocks, which typically use a 1.5Voltage cell, memory backup and wristwatches backup, most of which are very low power applications as well.
The cell voltage which is of nominal cell voltage for a nickel-based battery is 1.2Voltage, alkaline is 1.5V. The silver gets oxidised silver and uses 1.6V and lead acid uses 2.0Voltage. Lithium Primary batteries range between 3.0V and 3.9V.
The manganese and Lithium-based other systems often use cell voltages of 3.7V and at times even higher. This has very less to do with the chemistry of batteries than promoting a higher watt-hour denoted by Wh, which is made up of possible higher voltage. The argument here goes that an internal cell of low resistance keeps the voltage high under load. For operational purposes these cells use 3.6 Voltage.
Connection in Series
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The equipment which is portable which is needing higher voltages use battery packs with two or even more cells connected in series. Figure above shows a battery pack with four 3.6V cells which are in series, and are also known as 4S, specially to produce 14.4V nominal. In comparison if we see we notice that there is a lead of six-cell acid which is strong with 2V/cell will generate 12V. And there are also four alkaline with 1.5Voltage/cell and will give 6Voltage.
If you need a voltage which is of odd value of that is say 9.50 volts they connect five acid lead. Eight NiCd and NiMH or there are three Li-ion in series. The battery end voltage does not need to be exact as long as it is higher than the specific device. A 12Voltage supply might work in lieu of 9.50Voltage. Most operated battery devices can tolerate over-voltage. The end of the discharge voltage battery must be respected.
A very high voltage battery is kept the size of the conductor. The power on which Cordless power tools run on 18V and 12V batteries, their end which is high end models use 36 V and 24V. Most of the e-bikes or electric bikes which come with 36V Li-ion are 48V. The industry of car wanted to increase the starter battery from 12V or 14V to 36V, we better known as 42V, by placing lead acid cell 18 in series. The Batteries which are in remote and drones controls for hobbyists which is requiring high load current that often exhibit an unexpected drop of voltage if one cell in a string is weak. Drawing the current which is maximum stresses frail cells, leading to a possible crash. After reading the voltage a charge does not identify this anomaly, that is it is not examining the balance of or checking the capacity with a battery.
Parallel Connection
If a current is higher and is needed larger cells and these cells are not available or do not fit the design constraint. One or even more cells can be connected in the orientation which is parallel. Most of the chemical batteries allow parallel configurations with little side effect. Figure which is given below clearly illustrates four cells which are connected in parallel that are in a P4 arrangement. The voltage which is the nominal voltage of the illustrated pack remains at 3.60Voltage intact. But if we see the capacity in Ah and runtime we can observe that they are increased fourfold.
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A cell which develops a very high resistance or we can say that its opens is less critical in a circuit which is parallel than in a series configuration. But a cell which is failing will reduce the total load capability as well. It’s mostly like an engine which is only firing on three cylinders instead of on all the four. A lack of electricity on the other hand is more serious as compared to the faulty cell drains energy from the other cells, which is causing a fire hazard.
FAQs on Batteries in Series Parallel
1. What is the main difference between connecting batteries in series and in parallel?
The primary difference lies in how they affect the circuit's electrical properties. Connecting batteries in series involves linking the positive terminal of one battery to the negative terminal of the next. This configuration adds up the individual voltages of the batteries but keeps the total capacity (in Ampere-hours) the same as a single battery. In contrast, connecting batteries in parallel involves linking all positive terminals together and all negative terminals together. This method keeps the total voltage the same as a single battery but adds up the individual capacities, increasing the total runtime.
2. What happens to the total voltage and capacity when identical batteries are connected in series?
When you connect identical batteries in series, the main effect is an increase in the total voltage of the pack. The total voltage becomes the sum of the voltages of all the individual cells. For example, connecting three 1.5V batteries in series results in a total voltage of 4.5V. However, the overall capacity, measured in Ampere-hours (Ah), remains the same as that of a single battery in the chain.
3. How does connecting identical batteries in parallel affect the circuit's overall voltage and capacity?
Connecting identical batteries in parallel results in a circuit where the total voltage remains equal to the voltage of a single battery. For instance, connecting three 12V batteries in parallel still provides 12V. The significant advantage of this configuration is that the total capacity (Ah) and runtime are increased, as the individual capacities of the batteries are added together. This also reduces the total internal resistance of the battery bank.
4. How do you calculate the equivalent EMF and internal resistance for cells in series and parallel?
The formulas for calculating the equivalent electromotive force (EMF) and internal resistance differ for series and parallel connections as per the CBSE 2025-26 syllabus:
- For Series Connection: The equivalent EMF (E_eq) is the sum of individual EMFs (E_eq = E₁ + E₂ + ...). The equivalent internal resistance (r_eq) is the sum of individual resistances (r_eq = r₁ + r₂ + ...).
- For Parallel Connection (identical cells): The equivalent EMF (E_eq) is the same as a single cell (E_eq = E). The equivalent internal resistance (r_eq) is the individual resistance divided by the number of cells (r_eq = r/n).
5. Why is it not recommended to connect batteries of different capacities or ages in parallel?
It is strongly advised against connecting batteries of different capacities (e.g., a 50 Ah and a 100 Ah battery) or different ages in parallel. This is because the battery with the higher voltage or capacity will attempt to charge the weaker battery. This creates a continuous, wasteful discharge loop, which can lead to:
- Overcharging of the smaller capacity battery.
- Excessive heat generation, posing a safety risk.
- A significant reduction in the lifespan and performance of both batteries.
For a stable and safe parallel connection, all batteries should be of the same make, model, capacity, and age.
6. In what real-world applications would you choose a series-parallel battery configuration?
A series-parallel configuration is used when an application requires both a higher voltage and a higher capacity than a single cell can provide. A key example is in electric vehicle (EV) battery packs. Multiple cells are connected in series to achieve the high operating voltage needed for the motor (e.g., 400V or 800V), and then multiple series strings are connected in parallel to provide the high capacity (Ah) required for a long driving range.
7. What happens if a single cell fails in a series connection versus a parallel connection?
The outcome of a cell failure depends heavily on the connection type.
- In a series connection: If a single cell fails by creating an open circuit (like a broken link in a chain), the entire circuit is broken, and the battery pack stops delivering power completely.
- In a parallel connection: If a cell fails by opening, it simply stops contributing to the total capacity, and the pack continues to operate but with reduced runtime. However, if a cell fails by short-circuiting, it becomes a serious hazard, as the healthy cells will rapidly discharge their energy into the faulty cell, potentially causing overheating and fire.
