The truth about lithium batteries

A high quality battery. Its termination points are bolted into position to ensure nothing vibrates loose or breaks off internally. Its Bluetooth system lets you check on the battery’s health, current input/output, voltage, capacity %, cell temperature, charge status and a battery protection log. The BMS system allows the cells to be directly disconnected from terminals in the case of a short circuit or other emergency. A cell vent ensures that in the case of cell failure, each cell can vent any pressure and prevent thermal runaway.

Over the last few years a lot of interest and conversation has been sparked regarding using lithium batteries in boats. New technology and higher quality designs have come onto the market, but there is still is a lot of misleading information filling the social media airwaves. There are certain questions we get almost daily on the subject of using lithium batteries in boats.

      In this article I will compare lithium ion phosphate (LiFePo4) against the most commonly used battery in marine applications, the Absorbed Glass Matt (AGM). These two battery designs may look somewhat the same, but that is about where the similarities end!

      Since the early 1800s lead acid batteries have pretty much been the only reliable option when it comes to portable, low voltage power storage. The chemistry across all lead acid batteries is basically the same: positive anodes (lead) and negative cathodes (also lead) are submerged into an acid solution which stores power for you use at your discretion until the voltage becomes too low to run your appliance, and needs to be recharged.

      Over the years there have been a number of issues with the practicality of using heavy lead acid batteries, and manufacturers have been without the technology or resources to rectify these problems… until now!

A comparison between lithium and lead acid batteries.
Some battery systems come with a monitoring app for your smart device.
Here’s what’s hidden inside a cheap battery. It has thin, soldered terminals that can shake loose, and to save money it’s been put in a large case meant for a bigger model, making the footprint larger than it has to be. The small BMS (Battery Management System) is ineffective and unable to directly disconnect power in the case of a short circuit. The case is also poorly sealed, allowing water to enter.
This graph shows the decline in performance of a lead acid battery, compared with the steady output of its lithium counterpart.
Nowadays there are lots of models to choose from.
By switching from 2 x 12V lead acid batteries to a 24V lithium, and removing the on-board charger, Steve Morgan took 60kg of weight out of the back of his boat, improving its performance. The complete system cost around $4000, but Steve says he’d rather pay that than fork out for a bigger outboard.

      Lithium-ion batteries were first produced and commercialised in the 1990s, and have been the driving force behind nearly all your household, commercial and workshop electrical goods ever since. Their large storage capacity, light weight, safety, high discharge life cycles and the ability to be recharged fast makes them the perfect solution for powering anything from electric cars to hearing aids.

      Although the chemistry make-up of lithium batteries can differ from manufacturer to manufacturer, there are a few common components that make up majority of them. Graphite (anode) and Li-metal-oxide (cathode) make up the electrodes, and are encased in an electrolyte formula. Without getting too technical, the way that the lithium ions react in the charging and discharging processes is what makes these batteries much more efficient than their lead acid counterparts.

      One of the biggest key factors that sets lithium and lead acid apart is lithium’s constant output voltage. As shown in the diagram hereabouts, the voltage in a lead acid battery begins to fall almost immediately after it starts its discharge cycle – and most electronic devices will start to shutdown at around 10V (on a 12vdc circuit). This is well known to cause component damage due to ‘brown power’ or low voltage burn out. Not only is it damaging your components, but you are only getting around 40-50% usage out of your battery before it runs out of ‘safe’ power and your electrical device switch off.

      Lithium, on the other hand, has a consistent output supply voltage, delivering full voltage for up to 90% of the battery’s capacity to your electrical device. Once the battery reaches its safe discharge level (usually 80%-90%), it cuts all output power, leaving you with no ‘brown power’ and no low voltage spikes. This is why lithium batteries cannot be measured with a voltage meter, rather a percentage meter must be used (like on your mobile phone). Lithium is designed to deliver a full, steady voltage across its discharge cycle.


      When a good quality LiFPo4 battery is used in an electric motor application you can expect to notice a big difference in the motor’s performance, and here’s why!

      Your speed setting on your trolling motor controls are governed by a potentiometer. This means the higher the number on you controller, the higher the voltage delivered to the motor, the lower the number the lower the voltage.         Let’s say you motor operates at 100% @ 13vdc (voltage direct current), 50% @ 8vdc and 25% @ 4vdc. Because the voltage discharge curve of lead acid starts to decline as soon as you start to use it, you can expect your trolling motor efficiency to do the same. As you begin your day using your motor, the voltage in your battery bank is slowly dropping every minute you use it, lowering the efficiency of your motor almost immediately. What you think is 100%, now starts to decrease and within the first hour of your day, your motor could be running at as little as 80% (depending on battery capacity). But you get the picture!

      We often get complaints from anglers about how in windy conditions their electric motor will no longer hold on spot lock, and the angler drifts off their waypoint. In some situations, this has become dangerous. This is because at the start of the day they were running on 80-100%, then the motor worked hard during the day and the batteries were low. The motor was trying to give 100% but the batteries only had enough voltage to give, say, 25%. That’s not enough to keep you on your spot, and you get blown away with the wind.

      Because lithium does not have the big voltage discharge curve like lead acid, you can expect to be getting 90-100% of the battery’s voltage throughout its discharge cycle. So, at the day’s end you can expect to still have the same voltage output that you started the day with.


      Similar to the examples given for the trolling motor batteries, when cranking your motor with lithium batteries, you get an even output voltage without the big voltage drop like that of a lead acid. Electrical components such as starter motors, graphs, sounders and pump controllers rely on a steady voltage within set parameters. Most 12vdc components have a threshold from around 10.5 to 16.5.

      When you are cranking your combustion motor with a lead acid battery you will notice a high discharge voltage drop. This affects all components running off that battery; if the voltage falls below that of the set parameters the component will no longer operate, and switches off your device. When this voltage drop problem is not corrected it is often followed by starter motor and device failure.

      All electrical components run off a minimum wattage (volts x amperage). If the voltage is decreasing the amperage must increase to compensate. This puts more strain on your whole system. Although starter motors usually don’t have sensitive circuitry, the constant low voltage and high current draw eventually wears them out.


      If a lead acid battery is charged at a high rate it builds up resistance, due to the chemical reaction going on inside the battery. This is given off in the form of heat, which not only does long-term damage to your cells, but it also gives your system a ‘false float voltage’, which tells your charging system that it is fully charged prematurely. Once the battery has cooled and the float voltage drops, it then continues to charge. However, a hot battery can take hours to cool, and the whole process takes a lot longer than you may anticipate. This resistance issue is also present when a lead acid battery is discharged at a high rate.

      Because of lithium’s design characteristics, it has very low resistance when both charging and discharging. This enables it to accept a much higher charge/discharge amperage without compromising the battery’s integrity. In most cases a good quality LiFepo4 battery can be charged/discharged up to four times faster than that of a lead acid.

      High quality LiFePo4 batteries have an extremely low self-discharge rate and without memory build up, this enables LiFePo4 batteries to sit unused for long periods without discharging and without storing a low voltage memory like lead acid batteries commonly do.

      Basically, this equates to a battery that is lighter, has greater storage capacity, lasts much longer, delivers cleaner power, provides up to eight times more life cycles and can be charged quicker than a standard lead acid battery. This makes the total cost of ownership much cheaper than that of any lead acid. All these factors will obviously vary from manufacturer to manufacturer depending on the quality of their components and battery design.


      Researchers and developers of high-end LiFePo4 batteries have now shifted to a non-metallic lithium using lithium ions. Although slightly lower in energy density, the lithium-ion system is considered to be one of the safest batteries produced.

      Over the years, poorly constructed/ designed batteries have been the main factor in certain types of lithium batteries experiencing ‘thermal runaway’. This is when a cell starts to fail and gives off gases as it starts to heat up, and pressurizes the cell. If the cell has no ventilation and is sealed tight, the pressure and heat get greater and greater until the case cannot hold any more, and it ‘vents’ itself. As you can imagine, to keep the lithium batteries small and compact, some lithium batteries do not have any venting or protection devices integrated into them. This means the quality of the batteries’ components is the only protection offered in most cases to prevent thermal runaway.

      This quality issue is the same with larger lithium batteries. High quality manufacturers will only use quality materials and components for their batteries. The safest batteries on the market should have integrated a BMS (Battery Management System) into the battery. This vents the cells in case of thermal runaway, and they also have a multitude of circuit and cell protection components. Some manufacturers even give you the option of an in-built Bluetooth system that allows you to check the status of your battery via an app on your smart device, but don’t get this confused with the BMS. Bluetooth does not mean it is any safer or any better quality than the next.

      Lithium-based batteries have been around for some time now, and come in many shapes and forms. There are lots of different manufacturers and wholesalers more than willing to sell you a battery. However, unless you ask the correct questions and do your homework on the product, you may not get the safety and reliability you are looking for. The saying ‘a poor man pays twice’ runs true when it comes to purchasing a safe, reliable product.

      Different countries have different standards and rules around manufacturing and safety requirements of their batteries. Don’t believe for a second that they’re all as good as each other. I have heard numerous stories of online purchases that have gone horribly wrong, all because the customer didn’t do their homework and thought they were getting a ‘great deal’. To avoid this, make sure you get your battery from a company that complies with Australian standards for what you intend to use it for, has a reputation for producing a safe and reliable product, stands by their products and provides good back-up service.

      Like all batteries, quality LiFePo4 batteries still require the owner to provide certain precautions are met when charging and discharging. While they are maintenance free, your wiring and all circuitry still needs to be in good condition to ensure your safety is never compromised. So many people spend tens of thousands of dollars on the latest and greatest electrical components, fish finders, GPS systems and electric motors, only to skimp on the main force that is driving it all: batteries!

      I hope this article has helped a few people out, answered some questions, and made you keen to find out more!

      For more information do a Google search for ‘Sealed Invicta FAQ’, or visit the M&J Auto Electrical website.