So schalten Sie Batterien in Reihe und parallel

Connecting batteries incorrectly can result in reduced performance, premature cell degradation, or in serious cases, safety failures.

Whether you are designing a battery system for solar storage, industrial equipment, marine applications, or commercial EVs, understanding series, parallel, and series-parallel configurations is a fundamental requirement.

This guide explains each configuration clearly, with the technical detail needed to make the right decision for your application.

The Core Principle

Every battery connection decision comes down to two variables.

Stromspannung Undcapacity (Ah).

• To increase voltage, connect in series.
• To increase capacity, connect in parallel.
• To increase both, use a series-parallel configuration.

Batterien in Serie anschließen

How It Works

In a series connection, the positive terminal of one battery connects to the negative terminal of the next.

This continues until all batteries in the string are connected.

The total system voltage is the sum of all individual battery voltages.

The capacity remains equal to the capacity of a single battery.

Example

Three 12V 100Ah batteries connected in series:

Wiring Instructions

1. Connect the negative terminal of Battery 1 to the positive terminal of Battery 2.
2. Connect the negative terminal of Battery 2 to the positive terminal of Battery 3.
3. Connect your load or application to the negative terminal of Battery 1 and the positive terminal of the last battery in the string.

Connection order matters.

Always connect the negative terminal first and disconnect the positive terminal first.

This reduces the risk of accidental short circuits during installation and removal.

Voltage Ceiling and Safety

Series connections increase total system voltage.

At voltages above 50V DC, the risk of electric shock increases significantly.

Most regional safety standards classify 50V DC and above as hazardous voltage requiring additional protective measures.

For systems operating above 120V DC, which is the safe extra-low voltage threshold under EU standards, additional insulation, protective equipment, and qualified installation personnel are required.

Always verify the applicable electrical safety standards for your region and application before designing a high-voltage series string.

Key Requirements

All batteries in a series string must have:

• The same voltage rating
• The same capacity (Ah)
• The same chemistry
• Ideally the same age and cycle history

Mixing batteries of different voltages in series is not safe and will cause cell imbalance and potential damage.

Unlike parallel connections, capacity must match in a series string.

A weaker cell in a series string will be driven into over-discharge before the stronger cells are depleted, causing permanent damage to that cell and reducing overall system performance.

Charging Considerations

Charging a series string requires careful management.

If batteries in a series string have even small differences in internal resistance or state of charge, some cells will reach full charge before others.

Without proper management, the cells that charge first will be overcharged while others remain undercharged.

Recommendations:

• Charge each battery individually where possible
• If charging the series string together, use a Batteriemanagementsystem (BMS) with cell balancing capability
• Active balancing BMS is preferable to passive balancing for large series strings as it redistributes energy between cells rather than dissipating it as heat

Parallel anschließen Batterien

How It Works

In a parallel connection, all positive terminals connect together and all negative terminals connect together.

This increases total capacity while voltage remains the same as a single battery.

Example

Four 24V 50Ah batteries connected in parallel:

Wiring Instructions

1. Measure the voltage of all batteries before connecting. Proceed only when all batteries are within 0.1V of each other.
2. Connect negative terminals first, then positive terminals.
3. Connect all positive terminals together.
4. Connect all negative terminals together.
5. Connect your load from opposite corners of the battery bank. Take the positive connection from the first battery and the negative connection from the last battery. This distributes current draw evenly across all batteries and prevents individual cells from carrying a disproportionate load.

Key Requirements

All batteries in a parallel bank must have:

• The same voltage rating
• The same chemistry
• A state of charge within 0.1V of each other before connection

Regarding capacity:

Matching capacity is strongly recommended but is not a strict electrical requirement for parallel connections.

Batteries of different capacities can be connected in parallel provided voltage and chemistry match.

For example, a 12V 100Ah and a 12V 200Ah battery can be connected in parallel, giving a total of 12V 300Ah.

However, the smaller battery will reach full charge and full discharge faster than the larger one during each cycle.

Without a BMS actively managing this imbalance, the smaller battery will be overcharged and over-discharged more frequently, causing it to degrade significantly faster than the larger battery.

If you are connecting batteries of different capacities in parallel, a capable BMS is not optional. It is a requirement.

For the simplest and most reliable system, use batteries of the same capacity.

Internal Resistance and Current Sharing

When batteries with different internal resistances are connected in parallel, current does not distribute evenly between them.

The battery with lower internal resistance will carry a higher proportion of the current during both charge and discharge.

Over time this causes that battery to run hotter and degrade faster than the others.

As it degrades, its internal resistance increases further, which compounds the imbalance and accelerates the problem.

To minimise this risk:

• Use batteries from the same production batch where possible
• Never mix old and new batteries in the same parallel bank
• Never mix batteries of different brands or models in the same parallel bank
• Monitor individual battery temperatures in large parallel systems

Maximum Parallel Strings

For most applications, limit parallel connections to a maximum of four strings.

Beyond four strings, current distribution and thermal management become significantly more difficult to control.

Imbalances between strings are harder to detect and correct, and a fault in one string can affect the entire bank more severely.

For systems requiring capacity beyond what four parallel strings can provide, consult your Batteriehersteller or a qualified system integrator.

Fusing Requirements

Each parallel string must have its own fuse or circuit breaker installed as close to the battery terminal as possible.

Without individual string fusing, a fault in one string will draw discharge current from all other strings through the fault point.

Depending on the total bank capacity, this current can be high enough to cause fire or explosion.

This is a critical safety requirement for all parallel and series-parallel systems.

Charging Considerations

Parallel-connected batteries charge at the same voltage as a single battery.

A standard charger matched to the battery voltage will work correctly.

Charging time will be longer compared to a single battery because the total capacity of the bank is higher.

Confirm that your charger has sufficient current output to charge the full bank within an acceptable timeframe for your application.

Serie-parallel angeschlossene Batterien

How It Works

A series-parallel configuration combines both methods to increase voltage and capacity simultaneously.

Batteries are first grouped into series strings to achieve the target voltage.

Those strings are then connected in parallel to achieve the target capacity.

Example

Six 12V 50Ah batteries in a 2S3P configuration:

Key Requirements

In a series-parallel configuration, all batteries must be identical in voltage, capacity, chemistry, and ideally age and cycle history.

Each parallel string must be individually fused.

All strings must be at the same state of charge, within 0.1V of each other, before being connected in parallel.

Any imbalance between strings will cause circulating currents, leading to uneven charging, accelerated degradation, and potential safety issues.

A BMS capable of managing both series cell balancing and parallel string monitoring is strongly recommended for all series-parallel systems.

Choosing the Right Configuration

Critical Rules for All Configurations

1. Match voltage always.
Voltage must match for both series and parallel connections without exception.

2. Match capacity for series, recommended for parallel.
In series strings, capacity must match to prevent weaker cells from being driven into over-discharge. In parallel banks, matching capacity is strongly recommended but not a hard electrical requirement. Mismatched capacities in parallel require active BMS management.

3. Match state of charge before connecting.
All batteries must be within 0.1V of each other before connecting in parallel. A larger voltage difference causes high equalisation currents that can damage cells and generate dangerous heat.

4. Connect in the correct order.
Connect negative terminals first. Disconnect positive terminals first. This reduces the risk of accidental short circuits during installation and removal.

5. Fuse each parallel string individually.
Install a fuse or circuit breaker on each parallel string as close to the battery terminal as possible. This is a non-negotiable safety requirement for all parallel and series-parallel systems.

6. Use appropriate Kabeldimensionierung.
Size cables for the maximum current the system will carry with an appropriate safety margin. Under-rated cables generate heat, reduce efficiency, and create fire risk.

7. Use a BMS.
A battery management system protects against overcharge, over-discharge, short circuit, and thermal issues. For series configurations, active cell balancing is essential. For parallel configurations with mismatched capacities, a BMS is required.

8. Verify compatibility with your battery manufacturer.
Not all battery models support series or parallel connections. Some LFP-Batterien with built-in BMS units are not designed for external series or parallel connections. Always confirm compatibility before building a multi-battery system.

FAQ

Erhöht sich die Verstärkungsstunden parallel an die Anschlüsse?

Yes. Connecting batteries in parallel increases total amp hour capacity while keeping voltage the same. Two 12V 100Ah batteries in parallel produce a 12V 200Ah system, providing twice the runtime before recharging is required.

What happens when you connect two 12V batteries in series?

You get a 24V system with the same amp hour capacity as a single battery. If each battery is rated at 12V 100Ah, the series combination gives you 24V 100Ah. Voltage doubles, capacity stays the same.

Which is better, series or parallel?

Neither is universally better. The right choice depends on your voltage and capacity requirements. If your equipment operates at a higher voltage, series connection is necessary. If you need longer runtime at the same voltage, parallel is the answer. Many larger systems use series-parallel to achieve both.

Can LFP batteries be connected in series or parallel?

Most quality LFP batteries support both configurations, but this depends on the specific product and its internal BMS design. Some LFP batteries with built-in BMS units are not suitable for series connection because the BMS circuits are not electrically isolated from each other, which can cause ground loop issues and safety faults. Always confirm compatibility with your battery manufacturer before connecting LFP batteries in series.

What is the maximum voltage difference allowed before connecting batteries in parallel?

No more than 0.1V difference between any two batteries before connecting them in parallel. A larger voltage difference causes an immediate high equalisation current to flow between batteries when connected, which can damage cells, generate significant heat, and in severe cases cause safety failures. Always measure and match battery voltages before making parallel connections.