Category: Battery

Connecting multiple batteries is fundamentally done in two ways: parallel wiring or series wiring. But what’s the difference between these two methods? And which method best suits your needs? In this blog, we’ll explain everything about safely and efficiently connecting batteries on your boat.

What’s the difference between wiring in parallel and series?

The difference between wiring batteries in parallel and in series centres on how you affect voltage and capacity. Both methods have their advantages and applications.

Parallel connection

When connected in parallel, you link the positive terminals of the batteries together, as well as the negative terminals. The result? The voltage remains the same, but the total capacity (Ah) increases.

• Example: Two 12-volt batteries, each with a capacity of 100 Ah, together provide 12 volts and 200 Ah. This means you can store and use more energy without recharging in between, which is useful for prolonged use.
• Advantages of parallel connection: With a parallel connection, you benefit from a higher capacity without increasing the voltage, which is ideal for systems operating at a fixed voltage, such as 12V installations in motorhomes, boats, and solar energy storage. Because you can store more energy, you can use your battery bank for longer without recharging in between. Additionally, the load is distributed across multiple batteries, which benefits the lifespan and efficiency of the individual batteries. As the voltage remains the same, there is no risk of overvoltage, ensuring sensitive equipment continues to operate safely.

Series connection

When connecting batteries in series, you connect the positive terminal of one battery to the negative terminal of the other. This increases the total voltage while the capacity (Ah) remains the same.

• Example: Twee 12V-accu’s van 100 Ah leveren samen 24 volt en 100 Ah. Dit is vooral handig voor systemen die een hoger voltage vereisen, zoals krachtige omvormers, grote elektrische motoren of industriële toepassingen.
• Advantages of series connection: With series connection, you benefit from increased voltage, which enables more efficient energy consumption in heavy-duty applications. A higher voltage ensures that the current (Amperes) remains lower for the same power demand, leading to less power loss in cables and less heat generation. This makes it a suitable choice for situations where long cables are used or where efficient energy management is essential.

When do you choose to connect in series or parallel?

Your choice between series or parallel connection depends heavily on your energy requirements, the type of equipment you’re using, and your available space on board. When to choose parallel connection?

When to choose parallel connection?

• Extended usage time: Batteries connected in Parallel are perfect if you need power for an extended period, for example, for navigation lights, a fridge, or other onboard equipment. The higher capacity (Ah) allows you to use your battery bank for longer without needing to recharge in between.
• Flexible system expansion: By connecting batteries in parallel, you can easily increase capacity without changing the voltage. This allows for the expansion of an existing system, as long as the batteries are well-matched.

When would you opt for series connection?

• Higher voltage for high-power equipment: Sommige apparaten, zoals een 24V-omvormer, elektrische lier of boegschroef, vereisen een hoger voltage. In dat geval is serieschakeling essentieel.
• More efficient energy use and less cable loss: A higher voltage means you need less current (Amperes) for the same power output. This reduces current loss in the cables and makes the system more efficient.

Step-by-step guide to connecting batteries in series or parallel

Connecting batteries correctly is important for both performance and safety. An incorrect connection can lead to damage to your batteries or equipment. Below are step-by-step instructions for connecting multiple batteries in series or parallel.

General preparation

1. Check the batteries: Ensure all batteries are identical (make, type, capacity, voltage, and manufacturing date). Also, check that they are in the same state of charge (SOC) before connecting them. This prevents uneven loading and prolongs their lifespan.
2. Use the correct cables: Opt for identical, thick cables of sufficient gauge to minimise power loss and ensure stable operation. Ensure the cables are of equal length to prevent unequal resistance and loading.
3. Fuses and protection: Consider using fuses or a battery protector to prevent damage from short circuits or overcharging.

Connecting batteries in parallel

1. Install the batteries: Place the batteries side-by-side and ensure good ventilation to limit heat build-up.
2. Connect the positive and negative terminals: Connect the positive terminal of one battery to the positive terminal of the other, and do the same for the negative terminals.
3. Connecting to the system: Connect your load (e.g. an inverter) to the positive terminal of the first battery and the negative terminal of the last battery to achieve even current distribution.
4. Check the total capacity: Use a multimeter to verify that the voltage remains correct and that the total capacity (Ah) adds up.

Connecting batteries in series

1. Install and check the batteries: Ensure the batteries have exactly the same voltage before connecting them. This prevents uneven load.
2. Connect positive and negative: Connect the positive terminal of one battery to the negative terminal of the other.
3. Connect the remaining positive and negative terminal: Connect the free positive and negative terminal to your electrical system.
4. Check the voltage: Use a multimeter to check that the higher voltage is displayed correctly and that there are no deviations.

Common mistakes and points of attention

Whether you opt for parallel wiring or series connection, there are a number of common mistakes to avoid:

• Dissimilar batteries: Batteries with different capacities, voltages, ages, or chemical compositions can discharge and charge unevenly. This causes imbalance, faster wear, and a reduced lifespan for the battery bank. Always use identical batteries with the same specifications.
• Incorrect cable thickness: Cables that are too thin can overheat, cause extra resistance, and lead to voltage drop. This makes your devices work less efficiently and can cause the battery bank to wear out faster. Choose cables suitable for your system’s current rating and take cable length into account.
• No battery balancer: With lithium batteries, a battery balancer is essential to prevent individual batteries from being overloaded. Without one, the voltage between cells can become uneven, leading to overloading, faster wear, or even failure of individual batteries.
• Incorrect connection method: One of the most common mistakes is to connect all batteries in parallel and then connect one side of the parallel-connected battery bank to the electrical system. As shown in the illustration below:

Combining series and parallel

Combining series and parallel connections is a clever way to utilise both higher voltage and greater capacity. This is often applied in large energy systems, such as electric vehicles, solar energy storage, electric propulsion, and multi-system yachts.

How does series-parallel connection work?

Suppose you have four 12V 100Ah batteries:

1. Step 1: Series connection – Connect two batteries in series each time (positive terminal of one to the negative terminal of the other). This will give you two sets of 24V 100Ah.
2. Step 2: parallel connection – Next, connect the two series sets in parallel (positive terminal to positive terminal, negative terminal to negative terminal). This will keep the total at 24V, but double the capacity to 200Ah.

High-quality batteries from AB Marine Service

The choice between parallel or series battery connection depends entirely on your onboard needs. Do you want a longer run time per charge and greater battery capacity? Then opt for parallel connection. Do you need a higher voltage for powerful equipment such as an inverter or electric propulsion? Then series connection is the best option.

Whichever method you choose, ensure you install the batteries correctly, use identical batteries, and consider a battery balancer for lithium systems. By following these steps, you’ll ensure a safe and efficient onboard power supply.

Do you need help choosing or installing your battery? ? Feel free to contact the experts at AB Marine Service for professional advice and high-quality solutions. We’ll be happy to help. 

You’ve had a lovely day out on the water, the engine has been running nicely, and you assume your battery will be fully charged again. Yet, after a few days ashore, you notice the fridge is struggling, the lights are dimmer, or starting the engine takes just a little longer. How can that be?

Simple: your battery is probably not fully charged. And that’s not necessarily due to a broken battery or a fault, but often to the alternator. Or rather: to the limitations of what an alternator can do.

In this blog, we’ll explain why simply cruising isn’t enough to fully charge your battery, why AGM and lithium batteries require extra attention, and how you can achieve a full 100% charge with smart solutions.

Why your alternator isn’t enough to fully charge your battery

An alternator is perfect for quickly charging your battery while cruising; that initial part, the so-called bulk phase, is perfectly fine. However, to fully charge your battery (especially AGM or lithium batteries), a higher and more stable charging voltage is needed than a standard alternator provides.

But then it stalls. The final part of the charging process requires a higher and more stable voltage. Most alternators aren’t designed to properly charge the last 20 to 30%. This requires a stable, higher charging voltage, which most alternators can’t deliver. You often see charging voltages around 13.8V, while AGM or lithium batteries need 14.4V or more to charge fully.

Without an additional charging source, such as a battery charger or solar panels, your battery will never be truly full. And that carries risks.

Risk 1: Shorter battery lifespan

A battery that is never fully charged will deteriorate over time. With lithium batteries, problems can arise concerning voltage balance, and with gel or AGM batteries, sulfation will eventually occur. In both cases, this leads to a shorter lifespan.

Risk 2: Loss of capacity

A battery that isn’t fully charged will naturally deliver less capacity. This means less power for things like your fridge, bow thruster, or navigation lights. In other words, you’ll have to recharge sooner. Not ideal if you’re planning on staying at anchor for a while.

Risk 3: Starting problems and malfunctions

A battery voltage that’s too low can also be recognised by starting problems and malfunctions. Insufficient voltage can also lead to errors in sensitive onboard electronics. This is a serious risk, particularly on larger boats with all sorts of smart systems.

AGM and lithium batteries: why a higher charging voltage is crucial

In recent years, AGM and especially lithium batteries have become increasingly popular on board. It’s understandable: they’re compact, lightweight, and deliver a lot of power. However, these battery types also place higher demands on charging, especially if you want to charge them truly fully.

Both AGM and lithium batteries require a charging voltage well above 14 volts. Lithium batteries often need 14.4 to 14.6V, while AGM is usually between 14.2 and 14.4V. And not only that: this voltage must also remain stable during all charging phases, from the rapid bulk phase, through the absorption phase, to the trickle charge (float). This is the only way the battery cells can be properly balanced and fully charged.

Most standard alternators do not deliver such a high and constant charging voltage. The voltage often gets stuck around 13.8V and drops as soon as the engine speed decreases or the engine warms up. This may seem harmless, but with sensitive battery technology, it can lead to cell imbalance, overheating, loss of capacity, and ultimately a much shorter lifespan.

To keep your modern batteries in good health and make the most of their capacity, you’ll need a charging solution specifically tailored to AGM or lithium technology – such as a good battery charger, charge controller, or battery-to-battery charger (B2B charger) with the correct charging profile.

Smart charging with onboard chargers and solar panels

It’s therefore high time to make full use of the batteries. You can do this with boat battery chargers to charge stably via shore power or via free power on deck from solar panels. Charging your battery becomes a lot more pleasant with this.

Onboard chargers: stable charging via shore power

A good battery charger is essential on board. These devices supply the correct voltage and current, matched to the type of battery you are using. Where an alternator stops, the onboard charger continues.

As the charging process is controlled, the battery is neither overcharged nor undercharged. Many onboard chargers can handle multiple battery types: from traditional lead-acid to AGM, gel, and lithium batteries. Some models can even charge multiple batteries simultaneously, for example, a starter battery and a domestic battery.

However, you will need shore power (a standard socket) to use the battery charger. Additionally, ensure you use sufficiently thick cables, fuses, and proper mounting, especially considering the moisture, salt, and vibrations that are normal on board.

Solar panels: free power on deck

Another solution to get your modern batteries fully charged is by using solar panels. Thanks to the efficiency of solar cells, even a relatively small panel can make a significant contribution. Think about topping up your batteries while at anchor or even while underway.

Provided you have a good charge controller (preferably an MPPT controller), solar power can effectively charge even sensitive battery types like lithium or gel batteries. The right controller ensures the charging process is precisely tailored to your battery type’s requirements.

Of course, there are also some limitations. On grey days or in winter, the effect is limited, and you need sufficient deck space to install panels. Nevertheless, most installations today are so compact and user-friendly that they fit perfectly even on modest vessels.

What to consider when choosing the right battery charger?

As mentioned, correctly charging your battery does involve a few things. When choosing a boat battery charger, pay attention to the following points:

• Input voltage: Most battery chargers work on mains power (230V), but there are also models suitable for use with a generator or inverter. So always check where your charger gets its power from.
• Battery capacity: The required charging current depends on the battery capacity (in Ah). The larger your battery bank, the more powerful your battery charger needs to be. Guideline: choose a charging current of 10–20% of the total capacity. Do you have multiple batteries? Note whether they are connected in series or parallel, as this makes a difference to the capacity. Read more about connecting batteries in series or parallel here.
• Suitable for your battery type: Not every battery charger is suitable for every type of battery. Modern chargers can often be set for AGM, gel, or lithium batteries. Check if your charger supports the correct charging profile for the type of battery you are using. This ensures safe and full charging.
• Temperature compensation: A special charger can take temperature into account. This is useful in warm, humid spaces such as an engine room.
• Trickle charger: A battery charger with a trickle charge function is ideal if your vehicle is laid up for extended periods. It keeps your battery topped up without the risk of overcharging. Particularly useful during winter storage or if your boat is frequently connected to shore power.
• Marine grade build quality: Choose a charger that can withstand saltwater, vibrations, and other characteristics of a marine environment.

Conclusion: with the right charger, you’ll have a carefree sail.

With a fully charged battery, you’ll set off more comfortably. For safe navigation, sufficient comfort and, of course, safety, electricity is indispensable. Therefore, don’t just rely on your dynamo, but also invest in the right battery charger and possibly a solar panel system.

If you’re after tailored advice on your battery setup, or you’re looking for a reliable Victron battery charger for your boat, get in touch with the experts at AB Marine Service. We’ll be happy to help! 

When switching to lithium batteries for your boat or motorhome, one question is paramount: how do you safely charge them via the dynamo? At first glance, it seems straightforward. The engine is running, the dynamo is supplying power, and the battery is charging. In reality, it’s a bit more complicated.

Without a proper setup, it’s possible to damage the battery. The dynamo can also become overloaded. Especially for boat and camper owners who are replacing their old lead-acid batteries with lithium systems, we’ll explain the best way to approach this.

Why lithium batteries can’t just be connected to a dynamo

A lithium battery works a little differently from a traditional lead-acid battery. With a lead-acid battery, it accepts less current as it gets fuller, and the dynamo is gradually less heavily loaded. A lithium battery continues to draw a high charging current until it’s almost completely full. This means the dynamo has to run at maximum power for longer.

What’s more, lithium batteries need a precise charging voltage. While a bit of leeway is usually fine with a lead-acid battery, lithium ones will immediately cut out the Battery Management System (BMS) if the voltage strays too high or too low. Standard dynamos and regulators often struggle to control this effectively.

Should the engine speeds or temperatures fluctuate, the dynamo can overheat and the V-belt can slip. Consequently, the battery won’t charge properly. We’ll cover three dangers of directly connecting a lithium battery to a dynamo.

Dynamo overheating

If a dynamo keeps running at full power, it will get hot after a while. Especially when idling, as the dynamo gets very little cooling then. This can eventually cause damage to the bearings, windings and diodes. We’d rather avoid that, of course.

Overheating of the dynamo leads to a gradual process of reduced performance. The dynamo appears to still be working for a long time, but consistently supplies a little less voltage. Eventually, the dynamo will stop working. Proper regulation and protection prevent these problems.

Incorrect charging voltages

A lithium battery requires a stable charging voltage. For LiFePO4 batteries, the correct charging voltage is usually between 14.2 and 14.6 volts, depending on the make and BMS type. A standard dynamo with a built-in voltage regulator isn’t designed to stay within those tight margins. This can result in the lithium battery never reaching a full charge.

It may also be that the voltage rises too much at higher RPMs. If the voltage is too high, the BMS intervenes and interrupts the charging current. This can cause sudden voltage spikes in the vehicle’s electrical system and lead to damage to sensitive equipment or the starter battery. The correct charging profile and a specific voltage are therefore very important.

Dynamo or wiring overload

A lithium battery will keep drawing maximum current. This causes a standard dynamo to overload. Components such as the internal wiring, fuses, and connections aren’t designed for this. Eventually, the V-belt could even burn out.

Especially with boats that have older engines or motorhomes with thin cables running between the engine bay and the battery bank, this is a problem. Therefore, it’s important to have everything in order for the lifespan of your battery and other systems.

Two clever solutions: external charge controller or DC-DC battery charger

Ensuring the dynamo remains protected against overload and overheating can be achieved in two ways: with an external charge controller or with a DC-DC battery charger. We’ll happily explain more about these options for safely and responsibly charging your lithium battery.

Lithium batteries have a low internal resistance, allowing them to draw high currents when charging, especially in more modern vehicles with so-called ‘smart dynamos’. These are controlled by the onboard computer and don’t supply power constantly, meaning charging lithium batteries requires extra care. Therefore, it’s important to choose a suitable battery charger that performs well in different ambient temperatures and prevents the battery from being charged if it’s too cold or too hot.

Charging a lithium battery with an external charge controller

An external charge controller’s role is to replace or control the dynamo’s built-in voltage regulator. The system allows the dynamor to operate at full power, monitors voltage and temperature, and automatically adjusts the charging profile to suit the battery type. It adapts automatically to the conditions.

With an external charge controller like the Mastervolt Alpha Pro, the full output of the dynamo remains available and there’s no risk of overloading. It’s a sound solution, particularly for larger boats or systems with high energy demands.

Charging a lithium battery with a DC-DC charger

A DC-DC battery charger works a little differently. This charger is connected between the starter battery and the lithium battery. This way, the dynamo first charges the starter battery, after which the DC-DC charger controlledly passes current to the lithium battery. The charger determines how much current it allows through and keeps the charging voltage within safe limits. You can also set it with a maximum charging current to prevent overloading.

You can use multiple DC-DC battery chargers in parallel to get more power. This makes them ideal when working with multiple battery banks. They’re also a good choice if you have space and cabling limitations.

Which option suits your situation best?

Every installation is a bit different. When making the right choice when switching from a lead-acid battery to a lithium battery, it’s wise to take into account your current engine, dynamo, battery bank, and usage needs.

Choosing an external charge controller

We recommend opting for an external charge controller if you want to get the most out of your existing dynamo. This solution is particularly well-suited to larger boats with a high energy demand from a substantial battery bank.

Even if you sail for a long time and often, an external charge controller has a clear advantage. Because the dynamo can deliver its full power, it can simultaneously supply power to the battery and other systems without overload.

Choosing a DC-DC battery charger

If you’re after flexibility, for example if you’re working with multiple battery banks or different battery types, then we’d recommend a DC-DC battery charger. The charger can be set to regulate the charging current and voltage itself. This protects both the dynamo and the battery from varying engine speeds.

You’ll also need a DC-DC charger if you plan to add extra battery banks or expand the system later. This is because multiple chargers can be placed in parallel to increase charging capacity. For the DIY enthusiasts among us, this is therefore a sensible and flexible choice. You can also combine and expand different power sources with it. Overloading the dynamo is almost impossible with this setup.

Charging via a smart dynamo from AB Marine Service

Connecting a lithium battery directly to a standard dynamo, that’s not a good idea. Opt for an external charge controller or a DC-DC battery charger to safely and responsibly charge your lithium battery with a dynamo.

Do you have any questions about your situation? Don’t hesitate to get in touch with us. We’ll be happy to help you make the right choice. That way, you can soon be back on the water without a care, thanks to a modern battery system.