1 year on Lithium Iron Phosphate batteries on Impi, a revolution in lifestyle!

Many of you will know that about a year ago we installed 800Ah Lithium Iron Phosphate (LiFePO4) batteries on Impi. We are extremely happy with our installation which has enabled us to have a more enjoyable lifestyle on board Impi. We had ongoing problems with our AGM batteries, which are simply unsuitable for a world cruising boat in our view.

This may seem harsh but we had a totally unsatisfactory experience with our 8 AGM batteries with a poor warranty back-up from the manufacturer.

We left Fort Lauderdale with 8 brand new batteries which performed poorly by the time we got to Key West 3 weeks later. After a lot of discussion, the manufacturer agreed to replace them. This was after we spent an extra $1000 for an electrical report. By that time we were already in French Polynesia and it was impossible to ship replacements… sad but true.

lithium battery
2 400 Ah LiFePO4 battery packs from EV Power

Some of you may know that we went to explore a range of production catamarans  at the Cannes boat show and after a close inspection of their electrical set up decided to stick with Impi. It was very disappointing to see that these beautiful boats were equipped with electrical systems not suitable for world cruising and that all the factories we spoke to, did not give a lithium battery option. As such we have declined the opportunity to purchase such a boat as it would mean ripping out the whole electrical set-up as soon as the boat was built and paid for. We’ll just wait until manufacturers get their heads around technology which is now already years old.

One of the beautiful production catamarans we visited.

We continue to receive many questions from friends investigating an installation similar to Impi’s, so over the following days as a supplement to Brent’s interview with our secret weapon Jack Peters, Electronics Engineer for Outback Marine, I have transcribed some of their discussion for you all. here is the movie with lots of additional information. Lithium battery install

You can thank me later! We are actually fishing for flathead in Tasmania at the same time…. another thing Jack taught us!

So here are the areas discussed:

Jack, why would I want to consider LiFePO4 batteries as an option?

There are several benefits:

  • Can be charged and discharged faster – less engine runtime
  • More efficient – takes less energy to recharge
  • Can be cycled deeper – smaller battery will give the same useful energy
  • Take up less weight and space
  • Doesn’t suffer from sulphation, the cause of most premature failures with lead acid batteries
  • Longer life – replace batteries less often
  • Safety – Doesn’t emit flammable gases.

What do I need as a minimum to convert from for example AGM batteries to LiFePO4?

It depends on what you already have installed and how it is installed. So if you have programmable chargers on board already you should be able to program those for lithium batteries.

The other issue is where your charging equipment and batteries are located. So if you have batteries and chargers in your engine room, they should be relocated.

For Impi it was an easy transition as you had the right gear in the right place. More specifically you had Victron inverter chargers, which are programmable for LiFePO4 batteries by any skilled marine electrician. You also had Balmar regulator alternators, which again can be set to work with LiFePO4 batteries.

Most importantly, the location of your equipment was in the right place meaning they were in well ventilated cooler places which meant you did not have to put new cabling in and you had space to put in the management system and the isolators.

Other inverter chargers apart from Victron can also be used as long as they are programmable but we like Victron in that it is easily programmable and allows other external interfaces to plug straight into the management systems.

So someone who hasn’t got the right set up, what would they need to do?

They would have to evaluate what their needs are. For example do they need a bigger inverter to be able to heat hot water? Similarly they may choose to put bigger alternators on to have the ability to charge faster and minimize engine hours.

What is the reason for not wanting batteries or inverter chargers in the engine rooms? When we were in Cannes at the boat show all new production catamarans were doing this, Lagoon, Fontaine Pajot, Leopard…

No battery should be installed in the engine room, whether lead acid or lithium or other due to the increased temperature in the engine room.

Here is a table on the negative effect of temperature on battery service life for lead acid batteries:

battery life

Inverter chargers also will not perform very well in a hot environment. If you lower the temperature of the environment of an inverter charger by 20 degrees Celsius, it will improve performance by 10 to 20 percent and they will deliver power for longer.

The actual numbers for a Victron 12/3000 are:

25degC full output

40degC -10% output

65degC -30% output

This also applies to charging equipment in confined spaces. If the space is too small, you NEED fan forced ventilation.

So Brent why would the latest model production cats come out with all charging systems in the engine room?

Basically it is a set up aimed at the charter market so that the skipper doesn’t have to undo beds in guest cabins. However it is not technically justified and leads to inferior performance. In actual fact you would not want lithium batteries at all in the engine rooms.

So a lot of people are still worried that lithium batteries explode?

imagesThere are a lot of different lithium batteries. In other industries such as aviation for example where you see a lot of reported explosions and fires, they use a different type of lithium battery than the one we use in the marine industry. The batteries used in aviation have much more volatile and dense chemistries. In the marine industry we use LiFePO4 batteries. You don’t get as much energy in the battery for its space but its much safer. In actual fact the risk of thermal runaway is greater in AGM batteries.

What is thermal runaway?

It happens generally more in AGM batteries. If you have a discharged battery and you push in a lot of current, the temperature will rise and sometimes get to a point where it just keeps on increasing. Thermal runaway could take a battery to a point of explosion or excessive gassing.

AGM batteries are more susceptible to this than LiFePO4 as the latter have a very stable chemistry. In addition you have a management system, which would stop that from happening.

But LiFePO4 are expensive not?

As a straight buy they are, but if you are after performance and lifespan, they are not. You will not replace them as often. For a cost analysis per life span cycle please go to our technical page.

What is the worst-case scenario that could happen with LiFePO4 batteries?

When lithiums overcharge or over discharge the Battery Management System (BMS) shuts down the batteries meaning that the house bank is offline.

How can we build a system that in a worse case scenario avoids that the boat is without power, in other words how do we build in redundancy?

There are a number of BMS. The most common one is a high-powered battery isolator, remotely controlled. When the battery has an over voltage or under voltage it kills the battery bank.

On Impi, we have two battery packs, each with a BMS so if one pack fails, the other takes over. If there is a failure on one battery then the other still remains online. You might not even know that this happens.

However if there is for example a failure in the regulator of an alternator and you have an overcharge happening, that is going to knock both batteries down. Maybe one will go down slightly quicker and then the other will also go down which will leave you with two battery packs off line.

The simplest way to build in redundancy is to put in a switch that parallels your start system on to your main distribution buss. So the whole boat would go dark. Then, when you flick the switch, your lead acid battery from the starting system would connect to your buss running your loads.

The second way is that you could have multiple switches for all your different batteries, engine start, generator start and parallel them all up. You can then connect them remotely to a switch for example near the helm station. When you flick that switch, they all connect remotely via solenoids and bring the redundancy system online.

The third way is a little more complex and used in the Outback Marine Batteries. Basically we have 2 remote isolators and a third called an ACR, which stands for Automatic Charge Relay. The Battery Management System controls all three of them. It will basically switch the loads of the boat over to the engine starting system if it detects an over or under charge before it switches off the house bank so it is a seamless transition.

The Outback Marine Battery pack is 720 Ah, built up with 3 X 240 Ah cells. If one of the cells fails, then initially you switch over to the redundancy system, your engine start batteries. Upon reaching a suitable anchorage or in calm water, you can then determine which cell has failed and take that one off line. You can then bring the system back online but with a reduced capacity of 540Ah.

What are the charging systems on board Impi?

On Impi, we have an AC charging system (220V) namely generator and shore power and a DC charging system (12V).

The DC charging system comprises of 4 alternators, 5 solar panels and 2 Victron Inverter Chargers.

There are two big alternators one on each engine. Originally these were Balmars but due to continuous issues and no warranty back-up on their 150A range these were disposed off and replaced with the much cheaper Prestolites. These Prestolites deliver 170A each. They charge the house bank.

Overkill Electrics installing Prestolite alternators

There are two smaller alternators, one on each engine. They are Hitachi and deliver 80A each. They are required to charge the start batteries, but can be switched to charge the house bank in an emergency. However it is not desirable to have them continuously charging LiFePO4 batteries, as their internal regulators cannot be programmed for lithium style batteries and they would likely overheat and burn out.

On Impi, each Prestolite alternator has an external Balmar regulator and they are connected through a centerfielder. The internal regulator standard on Prestolite alternators is bypassed.

The function of the external regulator is to control the charge of the alternator into a 3-stage charge, bulk, absorption and float. You can program the regulator so that you have the charge rate for your particular batteries.


The temperature sensors, mounted on the external casing of the Prestolite alternators, are also connected to the external regulators and in case of over-heating, the regulator tells the alternator to throttle back the charge rate.



You also get temperature sensors on lead acid batteries, which will adjust the voltage according to the temperature measured. These were installed on Impi when we had AGM batteries but with lithium batteries they are not required.

The centerfielder is the device that controls both regulators to stop them fighting each other in a sense. It does that by detecting the output of each regulator and it selects the most efficient one. It then tells the other alternator to perform in the same way.

So the batteries are still charged by two alternators but in a sense are controlled by one regulator, the center fielder and both alternators receive the same signal.

The center fielder will also allow you to put sensors on the alternators and if there is a problem shut them down.

 The solar panels on Impi deliver up to 50A or as some people prefer to state 135W per panel. A Blue Sky MPPT controller, soon to be replaced by a Victron MPPT controller, regulates them. The benefit of having a Victron MPPT controller will be that all our DC inputs will be easier to monitor with one device, the Colour Control.


For lead-acid batteries, it is important to install the Victron MPPT Controller as close as possible to the batteries as it has a temperature function which registers the temperature of the environment the controller is based in and then sends a signal to the batteries to adjust voltage based on that temperature. If the controller is too far away from the batteries it may send an incorrect signal to the batteries based on the temperature it records, which may be different to the batteries’ environment temperature.

However, the location remains important as the device can only adjust for voltage loss in the cabling running from the panels to the controller and cannot affect the voltage loss in the cable between the MPPT controller and the batteries.

Finally there are two Victron chargers that deliver up to 240 A.So if all the charging systems were performing at peak, in theory 800A would be delivered to the battery bank. Lithiums would accept it, but a few fuses would pop…That would be too much charge. Batteries have ratings that are marked as C for Capacity in the instructions. A 100Ah battery, rated as 1C, would allow you to put 100 A into it for continuous charge.

The EV Power LiFePO4 batteries are rated at .5C so you can have an input of half the capacity of your battery. That means that on Impi we can have up to 400A in continuous charge.

What do the battery management systems on board Impi do?

The EV Power Battery Management System consists of two parts:

The Battery Control Unit (BCU) – one per battery pack of 400Ah, it monitors the battery voltage and the cell module loop and takes action to prevent charging and discharging if there is a fault.

The Cell Modules – one per cell act as stand alone shunt balances and link together to provide cell voltage monitoring.


The cell modules, which balance the voltage in EV Power batteries, are passive cell balancers. Basically they work in this way; if one cell has a slightly higher voltage than another it will loose a bit of energy in the form of heat to be in line with the other cells.

There exist also active cell balancers not used by the systems we describe, which will push the excess energy from one cell into another cell. They operate on a continuous basis and not just when the batteries are fully charged as is the case with passive cell balancers. However, passive cell balancers have much simpler and more reliable electronics.

In addition, Impi has a Color Control, a Multi Control and a BMV-702. Are they a  management system or are they just displays?

You can use them as part of your battery management system. The BMV-702 gives you the data for your batteries, Amps, voltage, state of charge so you know where you are in your battery use. You’ll know when you need to charge and when you can stop running the generator. You can program in alarms based on the state of charge, the voltage and the temperature.

BMV-702 on Impi

On the whole if you have a large battery bank and your available charge current is relatively small, then you are normally relatively safe as your charger cannot heat up the battery too much. So a lot of charging systems don’t have the ability to overheat batteries because of the size of the charger versus the size of the battery bank. That is one reason why you don’t want your batteries in your engine room, as the engine would heat the batteries’ environment in addition to the heat developed when charging.

So the BMV-702 has a relay on it?

Yes the unit has an audible alarm, a buzzer. You can also wire up the relay to an external audible alarm or a flashing light somewhere else. You can also wire up the relay to an action through hooking it up to a solenoid to turn for example your inverter charger off. For advanced units like the Victron Multiplus, there are inputs that will take this signal directly.

On Impi this was not done as you have two additional BMS on the batteries, which take care of that.

And the Multi Control? What does it do?

 It is convenient as you can easily see the charge state from the LED and you can easily turn the units on and off with the switch. It also gives you the ability to adjust your input limits if you are switching between different input sources e.g. shore power and generator. Turning the dial does this.

Multi Control on Impi

What is the specific function of the Color Control?

The Color Control connects to the Internet if you have a router installed on the boat or if you have a Wi-Fi dongle. It’ll pass all the data to a portal, which is a free-hosted system from Victron.

Color Control on Impi

This allows people with a User ID and password to look at the energy consumption on Impi, inputs, outputs and State of Charge. This would allow an engineer like me to trouble shoot the system from a far. It also allows pinpointing intermittent problems as the system logs the data. You can for example look back at the last month’s data and establish what is going on.

What are the benefits of an external battery management system over an all in one LiFePO4 battery such as Relion for example?

With an all in one battery system, the BMS is generally not accessible. There is a lot of variation in the quality that is being used and in the actual hardware that has been put in. There is also variability in the ratings, whether it can deliver the full current that you would expect from a lithium battery.

Generally, also the heat inside the battery can be problematic.

Finally, one needs to consider how easy it is to replace the cells. The simplicity of both EV Power and Outback Marine batteries are that one can unbolt the old cells and replace them with new ones. That way you retain part of your initial investment.

What is the difference in charging AGM and lithium batteries?

It is important to understand the difference between bulk, absorption and float charging for batteries. Simply explained the different stages of charging explain the ability of a battery to absorb charge.

Bulk charging means that the battery accepts as much amperage as your charger is rated for.

For most AGM batteries the number of amps going into the battery bank should not be greater than 30% of the capacity of your battery.

In the case of LifePO4 in bulk charging we can charge a 400Ah battery pack with around 200 amps in bulk charging stage.

During bulk charging, the voltage of the battery will increase from where is was before the charging, to the absorption voltage. The chargers will deliver their maximum current. For LifePO4 this voltage should be 14.2V and definitely no higher than 14.6V. For AGM batteries the voltage is between 14.4 and 14.8V. As soon as the charger reaches the absorption voltage, the bulk phase is over and absorption begins.

During absorption phase, the voltage will stay constant at the absorption voltage, and the current will decrease. LifePO4 batteries are around 95% full when absorption begins. This depends on the ratio of battery capacity to charge current, but for most systems with high power chargers absorption will last in the order of 10mins. It is important to note that most chargers have minimum times on their absorption phase, so the charger will stay in absorption longer than is required, but this will help passive balancing systems to work.

However for AGM batteries the absorption stage kicks in when the battery is around 80% full. This is one reason that AGM batteries take longer to charge than Lithium batteries. There is a lot more time spent charging with a diminishing charge current. The last remaining 20% of an AGM battery take much more time in comparison with the first 20% during the bulk stage.

The batteries achieve float stage when they are at about 100% charge. In float, the voltage drops for AGM batteries to 13.2-13.8V and for LifePO4 to 13.6V. Holding the batteries at a float voltage will offset any self-discharge, and make sure that the charger is supplying any loads on the system.

With AGM batteries the charge voltage is adjusted depending on the temperature. This doesn’t happen with lithiums.

What have you learnt in the 1 year on lithiums?

Keep the system as simple as possible, build in redundancy for your lithium batteries with your engine start batteries and have powerful charging systems that allow you to charge your batteries rapidly. Cheers!

Interview conducted by Brent Grimbeek, transcription Ana Hill



  1. Hi Brent, thanks for your thoughts, very useful. You missed on the boatshows that Outremer is fitting lithiumbatteries on their models. Outremer places them im the saloon. On our 45 to be delivered this summer we have two 200Ah lithium batteries from Mastervolt, we are impressed by your 800 amps!


    Liked by 1 person

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