The power of Lithium

One of the important decisions we had to make for Wildling, was the design of our on-board power systems. The traditional way to power a cruising sailboat at sea is to install a large house battery bank, typically comprised of 500 – 1000 Amp hours of lead acid batteries that will power all the ship’s systems. Many systems such as refrigeration, radios, instruments, autopilot, lights, pumps and winches are powered directly from the batteries, usually at 12 volts DC. Other systems such as the battery charger, water heater, air conditioning, microwave, and miscellaneous appliances need AC power which can be provided by running a diesel generator or via an inverter which converts DC power from the batteries to AC power.

There are some really important choices here and making the wrong ones can lead to a lot of extra weight, cost and complexity. Before I go into the details, let me start by laying out the objectives for an ideal electrical system.

The power systems on a cruising catamaran need to be:

  • Simple – we want to avoid complicated troubleshooting and repairs at sea if something goes wrong
  • Flexible – we need to be able take advantage of shore power at the marina, yet be autonomous at sea and at anchor
  • Reliable – the system needs to just work, and keep working for extend periods of cruising through many, many charge/discharge cycles
  • Lightweight – batteries are very heavy, so are generators. The combined weight of the two systems on our last boat was over 600 kg 1,300 lbs! We want to keep this to a minimum

Thanks to the electric car industry, Lithium-Ion battery technology has now matured to a point where traditional lead acid batteries (including Gel and AGM type batteries) no longer have any place on-board a cruising catamaran.

Here’s why:


Lead acid batteries are no longer a good solution for powering a catamaran. They are heavy, they take up a lot of space,  they can’t be discharged below 50%, they have a limited lifespan of 4-6 years, and they are slow to recharge. The slow recharging time (10+hours) is one of the biggest problems, because you either need a lot of solar or wind generation to recharge them (not always available) or you have to run the engines for long periods of time (expensive). Many folks install diesel generators in order to keep their lead-acid battery banks topped up, which makes a bad situation worse.


The contrast with lithium is enormous. Lithium batteries weigh less than half of lead-acid and take up half the space. They can discharge down to 80%, last 10+ years, and here’s the best part, they can be recharged as quickly as you can throw current at them. So if you have 400 amps of alternators, you can recharge a 500 amp hour battery bank in 1 hour!


Because of the rapid recharging ability of lithiums, we were able to design our power systems on Wildling to meet all of our needs without a generator. We will have 700 Watts of solar panels, a 600 Watt hydro-generator and 5,000 watts of alternators on the two engines. This gives us a lot of flexibility to run the systems we need and take full advantage of our green energy power systems to recharge the batteries, so no available sunlight or hydro-power is wasted. When needed we can run the engines for limited periods to top up the batteries. And by removing the need for a generator and using the lighter lithium batteries we save 480 kg (1,056 lbs)!!! And since less weight means we can sail more in lighter winds, we will run the engines less and save even more!


Over the past few years, many of the ocean racing sailboats have been testing out hydro-generators. They have been refined to a point now, where they are quite reliable.


This is the hydrogenerator we are installing on Wildling. It is lowered down when underway to produce up to 600 watts of power

A word of caution about these generators! There are two versions, a cruising version and a racing version. The cruising version operates in a speed range of 5 to 10 knots and the propeller will strip out if it’s driven at higher speeds. The racing version works at 8 knots to well over 15 knots. We are installing the racing version on Wildling.

The hydro-generator engaged when underway. Owners I have talked to that use this system say they don’t feel any effect on boat speed when it’s in the water. The racing version has a speed sensitive, variable pitch propeller so it’s very efficient.

There are very few technology choices on a boat that have as many positive benefits as lithium batteries. If you are buying a new boat or your house batteries need to be replaced, then go with lithium!

14 thoughts on “The power of Lithium

  1. Hi. We have a Watt and Sea 600W hydro solar generator and converter and 24V Lithium batteries. Any suggestions on how to connect these up?

    • Hi Mark,

      They are pretty straight-forward to install. The Watt & Sea user manual has good instructions on how to connect the generator to the batteries. Is there a specific problem you are having with your installation?

  2. Hi Doug how do you heat the water on board when at anchor. I presume if you have the engines running the heat exchanger will do the job.


    • Hi John,

      Yes, we use the engines to heat water when at anchor. If we’re using a lot of power we will run the engines for a bit to charge, and heat water at the same time, otherwise we run the port engine (which is connected to the heat exchanger) to heat water when we need it.

      • Thanks Doug. I am in a similar position to you only 12 months behind. We sold our Catana 581 recently in Florida and are looking at the 5X now with our UK friends and boat partners. I too am Australian. I have read all your posts with interest. Having never commissioned a new boat build it is a bit daunting with the extra options available.

  3. Hi Doug,

    Gary here with more questions for you. I have been reading the big debate on Cruisers Forum on LFePO4 batteries. One of the links referenced is the following:

    Based on this article the success of Lithium on boats is really rooted in the overall set up of the entire charging system. Thought I would ask you about the installation Outremer did and if you are happy with the system and still feel it was the right choice?

    Also, one of the boats I am considering is the Slyder 47 which has a hybrid power option. In fact hulls 4 – 7 are all being built with electric sail drives. Based on your experience would you consider electric drives with a diesel genset? This set up also enables power generation when under sail by the sail drives. It would be interesting to look at the overall weight of the hybrid system with the genset verses diesel engines without the genset..


  4. Hi Gary,

    Regarding lithium:

    I agree with your research. It’s critical to have a very robust cell protection and charging system for Lithium battery banks. There are three options that I am aware of.

    1. Buy the batteries from China (seems like they are all made in China anyway), then purchase the protection electronics and charging components, and put everything together yourself. This is by far the lowest cost option, and it seems you can get Lithium banks for around the cost of an equivalent lead-acid bank. The risk is that you do not have a proven design, and you may have reliability issues. Lithium batteries can explode if not protected properly, and I wonder what the insurance companies would do in this situation.

    2. Purchase the complete system from a single vendor. This is what we did. I estimate doing this cost us double what option 1 would have cost, but since our objectives are long distance ocean sailing, I was willing to pay the premium to have a proven reliable system from a single manufacturer. We chose Mastervolt. I have used their gear for years, and it’s always been good, and Outremer has a close relationship with them, has found them very reliable on previous boats, and can remotely troubleshoot any system issues if needed. I only have 6 months experience with our Mastervolt Lithium system, but so far it’s been flawless.

    3. Go with a 3rd party system configuration vendor. There are plenty of these around, since the price delta between options 1 and 2 is so high. You will save some money and the 3rd party system could be OK, but you have a greater risk in terms of reliability and suitability of the components they have selected, and it could be an issue to get service when it breaks in some remote location.

    Regarding Slyder 47 and Hybrid power:

    I like the Slyder boats a lot. They are one of the few manufacturers that are building performance oriented ocean cruising cats, that are well designed, although I don’t like their aft helm position.

    As for hybrid drives, I think it depends on how you want to use the boat and what problem you are trying to solve. If you are only doing short distance coastal cruising, then hybrid drives could be an option. Motoring distances are short enough that you can use your batteries a fair amount, and you typically have long periods in between use to recharge via solar. In this situation you would reduce your diesel consumption and reduce noise and vibration when motoring.

    But if you intend to do ocean sailing, I would not consider hybrid drives for two reasons:

    1. Too heavy: the size of the generator required to give true engine autonomy + the weight of the drives + the weight of the charging systems + the weight of the batteries + the weight of the motor cooling systems is more than the equivalent diesel engines

    2. Too complex, and hard to fix when they fail. There is a lot more technology needed to reliably run hybrid electric drives, and when (not if) the system fails, you will need access to expertise and parts to fix it. If you are in a remote location that might be next to impossible. It’s hard enough to find a Yanmar or Volvo repair person in many parts of the world.

    I think with both lithium and electric engines the choice is ultimately driven by your risk tolerance and how far from land and repair facilities you’re planning to take your boat.


  5. Any issues or concerns with thermal run-away on these batteries or is that not a typical problem? If so, I wonder if they can be extinguished with water.

    • Hi Bryan,

      Yes there are issues with thermal run-away in lithium batteries. The most important part of the lithium system is not the battery cells, it’s the charge management and protection technology that is being used. In practical terms, this technology seems pretty mature now, so there are very few cases of marine installations catching fire. I know quite a few people that have configured their own lithium systems using cells from China and 3rd party management and protection modules. These seems to work well, and cost a lot less than the integrated systems available from the mainstream vendors like Mastervolt. We went with a fully integrated Mastervolt system just to be safe, but it was expensive.

      As for how to extinguish a lithium battery fire onboard a boat, I honestly have no idea what would work best, but I really should know, and have extinguishers on hand that can handle it. I will do some research and report back.


  6. Hi Doug,
    Would you comment on running air-conditioning/heat? Without a genset, how long can you run your ac, and how many sections of the boat can be set to cool at one time? When you’re cooling the interior, what other systems can run on battery only?

    • Hi Mark, unfortunately I don’t have a lot of data on this yet because we haven’t been in any conditions where we have needed to run the air conditioning at sea or at anchor. We did some testing at the dock and we can easily run one of the zones (a cabin or the salon for example) with just the output of the solar panels or the hydro-gen. I need to verify this at sea and I will post data when I have had a chance to do more testing.

      • Hi Doug, With a little over a year since your last comment on the air conditioning without Genset, do you now have any additional observations? Have you been able to run air conditioning from inverter/battery bank?

      • Hi Tony, yes the air conditioning runs fine from the inverter, but since we have never needed it when away from a marina I don’t have any information on how much power it uses and how our batteries will handle it. My intent was not to use it at sea, only when we are at the dock.

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