The power of the right battery

Do you recognise the problem that when anchoring overnight, you already start calculating how long your fridge can stay on before you have to turn off the power? Or do you just want to be off-grid for longer, exploring your horizons without worrying about battery capacity? Then we have the solution for you.

At Smartmarine, we offer everything to be off-grid with your boat, including the powerful LiFePO4 (lithium) batteries, which in combination with our high-quality Electromaax alternators and our solar panels are perfect for long-term, reliable energy storage.

On this page, we explain to you the basics of the different battery types and focus mainly on the advantages of LiFePO4 batteries. How do you know which battery best suits your boating? No worries, we are happy to help! After all, the right battery and battery capacity can make the difference between carefree sailing or anchoring full of stress over power failures.

To make an informed choice for your on-board power system, we will list the pros and cons of lead-acid batteries, AGM batteries and lithium batteries. 

We only sell the lithium batteries because we really think it is the smartest choice and we stand by it completely.

Off the grid

Content

Battery types and their characteristics

Lead-acid batteries

The traditional choice, the lead-acid battery, has proven its worth over the years. This type of battery is reliable, cost-effective and works under a wide range of conditions. It is still one of the most common battery types on boats, mainly because they are relatively cheap to begin with.

Advantages:
  • Low purchase cost, making them attractive to sailors on a tight budget.
  • Reliable performance under normal use.
  • Easy to recycle.

Disadvantages:
  • Limited service life and charge cycles. This means they need to be replaced relatively quickly compared to other battery types.
  • They are heavy and large, which is detrimental to on-board weight distribution.
  • Very sensitive to deep discharge, which can drastically reduce their lifespan.
  • Not suitable for sailing under an incline, which can be a disadvantage on a (sailing) boat.

AGM batteries (Absorbent Glass Mat)

AGM batteries are an improved version of lead-acid batteries and offer some key advantages. They are low-maintenance, fully sealed, and can be placed in different positions. This makes them popular with sailors looking for a more robust and reliable option, without switching directly to lithium.

Advantages:
  • Little to no maintenance required.
  • They are safer than traditional lead-acid batteries as there is less risk of leakage.
  • Resistant to vibration and shock, which is a great advantage on rough seas.

Disadvantages:
  • Higher cost than traditional lead-acid batteries, though you pay for better quality and performance.
  • Still heavier and larger than lithium batteries, making them less suitable for situations where weight is an important factor.

Lithium / LiFePO4 batteries

Now for the gamechanger: the LiFePO4 battery. This modern powerhouse offers unparalleled performance and energy density. Compared to lead-acid and AGM batteries, LiFePO4 batteries last much longer, can be discharged deeper without performance loss, and handle high currents better.

They are the ideal choice for those who want to live seriously off-grid or spend longer periods of time on the water without worry. It is therefore common for customers to say, after switching to lithium, 'I wish I had switched sooner!'

Advantages:

  • Lightweight and compact: on a boat where every kilo counts, this is a huge win. It helps the overall performance and stability of the boat.
  • A much longer life, with significantly more charge cycles than lead-acid or AGM batteries. You don't have to worry about your battery giving up after a few years.
  • Faster charging and higher discharge capacity, meaning you can get more out of your power supply without draining your battery quickly.
  • Can be placed in different positions, and can be used under an incline without any problems, perfect for boats in rough conditions.
  • No maintenance required, leaving you more time to enjoy sailing instead of tinkering with your batteries.

Disadvantages:

  • Higher initial cost: lithium batteries are more expensive to buy, but the longer life and better performance make it an investment that pays off in the long run.
  • Sensitive to extreme temperatures: they should always be used in conjunction with a Battery Management System (BMS) to prevent damage from high or low temperatures.


There is another feature that needs some explanation, namely that LiFePO4 batteries are powerful and smart, especially thanks to the built-in BMS (Battery Management System).

BMS (Battery Management System)

This clever system sometimes brings additional concerns. We are happy to explain why this is not something to worry about and how you can easily make adjustments to enjoy the full benefits of LiFePo4.

Because LiFePO4 batteries can be discharged deeper and handle high currents when charging and discharging, you may need to modify some parts of your electrical system.

1. Charger
Fortunately, most modern chargers, such as shore power and MPPT chargers, already support a lithium charging profile, or allow you to create one yourself. Your charger might not do this. If you have any doubts whether your current charger is suitable, feel free to contact us. We are ready to advise and help you with any modifications.

2. Dynamo
Whereas a standard alternator is fine for charging a lead-acid starter battery or service bank, a LiFePO4 battery demands more from the alternator. The LiFePO4 can even overcharge the alternator and, in extreme cases, cause it to burn out. How quickly this happens depends on usage, but that it will happen is certain.

You are probably now charging your starter battery and service bank via a diode bridge, such as an ArgoFET. This system works well for lead-acid batteries, but will cause previously mentioned problems when charging LiFePO4.

Fortunately, there are excellent solutions to avoid this problem to suit everyone's needs and budget.

Read below for two options for charging your Lithium batteries with alternator.

The BMS is indispensable

This electronic system ensures that your battery is protected against overcharging, over-discharging and overheating. The BMS also monitors the status of your battery, such as voltage, current, temperature, and charge level, and ensures that the cells of your LiFePO4 battery are evenly charged and discharged provided it has a balance function.

A BMS ensures safety and significantly extends the life of your lithium battery. Without a BMS, the battery can overheat or even cause dangerous situations such as fire. Therefore, it is essential to always use a BMS in combination with a LiFePO4 battery.

Charging lithium battery with dynamo

The simple solution

The cheapest option is to remove the diode bridge from the system. Instead, charge the starter battery directly from the alternator, and fit a DC-DC charger (e.g. a Orion 30A) between the starter battery and your service bank. The alternator is not overloaded, and your starter battery charges safely. Your service bank is recharged via the starter battery by means of the DC-DC charger.

Disadvantage: This solution can be slow, especially if you have a large lithium bank. It might take days to fully charge it, as your current alternator is unlikely to provide enough power.

The advanced solution

Want to charge faster and get the most out of your system? Then opt for a new alternator, such as an Electromaax alternator, which charges your service bank directly. In this setup, the starter battery is charged from the service bank via a DC-DC charger. This is the most efficient solution, capable of delivering 120 amps to your service bank with ease, for example.

This option has a different price tag, but the benefits - fast charging and no overcharging of your alternator - make it well worth the investment.

More information on alternators can be found here and about DC-DC chargers here.

Battery capacity in Ah

Batteries are expressed in Ah, which stands for Ampere-hour. This indicates how much current a battery can deliver over a given period of time.

Suppose you have a 100 Ah battery. In theory, this battery can:

  • Delivering 100 amps for 1 hour.
  • Or deliver 10 amps for 10 hours.

To translate this into a practical example:

if your fridge draws 6.5 amps, a 100 Ah battery could run this fridge for about 15.4 hours (100 / 6.5).

Note: This is purely theoretical and assumes the battery 100% is full and fully discharged.

Lead-acid batteries

For lead-acid and AGM batteries, you should only discharge the batteries to 50% of their capacity to prevent damage and extend their life.

This means that a 100Ah lead-acid battery actually has only effectively 50Ah usable.

So, in the case of a 100 Ah lead-acid battery, you can only use it up to 50 Ah.Your 6.5 amp fridge can now run for only 7.7 hours, instead of the aforementioned 15.4 hours.

In addition, the efficiency of a lead-acid battery decreases the less full it is than 100%. The lower the charge, the worse the performance, and the faster the battery deteriorates in quality.

LiFePO4 (lithium) Batteries

These batteries can be discharged between 80-90% of their total capacity, without sacrificing life or performance!

We will assume the example is 80% usable. So, in the case of a 100 Ah lithium battery. You can effectively use 80 Ah. That means your 6.5 amp fridge can now run for about 12.3 hours.

Comparison in use 6.5 A fridge

Battery typeUsable capacityOperating time
100 Ah
lead acid		50 Ah7.7 hours
100 Ah
lithium		80 Ah12.3 hours

As you can see, a lithium battery allows you to supply power for much longer without damaging the battery or losing its efficiency. This is one of the reasons why we love lithium batteries so much.

Lithium batteries

View all lithium batteries
Victron

Victon is known for their high-quality technology and excellent compatibility within their range. Their lithium batteries are designed for optimal communication with other Victron products, although a BMS must be purchased separately.

Solar Mobile

Solar Mobile is an excellent price-conscious choice. These batteries are of high quality and come with a built-in BMS. They are easy to install and have an optional heat element for use in cold conditions and/or a Canbus for Victron connectivity.

Ready for carefree cruising?

At Smartmarine, we understand how important the right battery is for your adventures on the water. Whether you want to keep your old lead-acid system or buy a modern LiFePO4 battery, we are happy to help you find the best solution for your situation. Our team is always ready to advise you and make sure you can enjoy feeling free on your boat off-grid with peace of mind.

 

Need help? We're here for you!

Questions about batteries or other products? Feel free to contact our expert team. At Smartmarine, we are all about service and satisfied customers. We are happy to advise you so that you can sail carefree and without annoying annoyances.

 

Ask us for advice