Should I use lithium-ion batteries for my boat?

The way the batteries are designed these days makes them a lot safer, as does the electronics that monitor their health and wellbeing as they’re getting used, and as they’re being recharged.

The technology has advanced so far that all of a sudden, a bank of lithium-ion batteries is a viable alternative to an onboard genset on larger sports cruisers and motor yachts, not to mention more environmentally friendly and quieter.

But even small boat owners can reap heaps of benefit from thinking about jumping to lithium-ion batteries.

Helping to drive the technology is a new generation of electric outboard motors that depend on cutting-edge and affordable lithium-ion technology to make them viable.

Here are the reasons we think a switch to a lithium-ion battery makes sense.

This is always going to be the biggest pain point with lithium-ion technology. Expect to pay around double what you’d expect to pay for an equivalent lead-acid or gel battery with the same number of amps.

However, bear in mind that a lithium-ion battery has much more useable capacity than an equivalent-rated traditional battery.

This is because while you can safely use up to 50 per cent of its capacity, a lithium-ion battery can discharge up to 80 per cent of its capacity before needing a recharge.

That means if you replace a lead-acid battery with a lithium-ion equivalent, you get more than half as much more useable battery capacity.

The lithium-ion battery will also last a lot longer than its lead-acid equivalent. This is in part because you don’t need to rush back home to put the battery on the charger – the lithium-ion battery won’t be damaged and “remember” a short charge like a traditional one will.

The operating life of a well-maintained lead-acid battery is around four years, while for a lithium-ion battery that number jumps to about 10 years, even if you’re a bit lax about keeping up a regular maintenance regime.

A lithium-ion battery can be cycled up to 3000 to 5000 times, which over 10 years equates to whacking it on the charger for anywhere between 25 and 40 times a month without causing any problems. A lead-acid battery has about a third of the recharging cycle capacity before it starts to lose holding power.

A lithium-ion battery weighs around half as much as its lead-acid equivalent. That means for a boat running a starter battery and a house battery, both batteries combined will weigh around the same as a single battery that they replace.

However, because a lithium-ion battery has more useable capacity, you may not even need to replace a like-for-like battery.

Where a 100 amp hour lead-acid battery discharging to 50 per cent may have provided the power capacity you needed, a 50 amp hour lithium-ion battery discharging to 80 per cent may do as good a job of handling all the less vital onboard power requirements.

In that sense, a much lighter and more compact lithium-ion battery could easily run as a house battery to look after electronics, while the larger one can act as a cranking battery.

The other benefit of lithium-ion technology is the packaging. The batteries used in marine applications are fully weather-sealed, so you can use them anywhere you would have used a marine-rated lead-acid battery.

But where a lead acid battery has to be stored upright, a lithium-ion battery can store any which way, even upside down. That means the battery can be housed in a part of the boat that minimises the amount of space it takes up. The days of having a dedicated battery locker taking up a large part of the transom are gone.

Remember, too, how we said you could replace a 100Ah lead-acid battery with a 50Ah lithium-ion one? A 100Ah lithium-ion battery is about half the weight of the lead acid equivalent, so a 50Ah lithium-ion battery will be about half the size, and weight, again.

So instead of needing space for two batteries, you only need space for one and a half.

What's even more convenient is the shape in which you can package the battery. Choices are the traditional car battery, or for modular applications, you can get long, narrow batteries. All of a sudden you're not constrained to housing a big, bulky block.

Lithium-ion technology has been part of the automotive space for some time now, so adapting alternator-based charging for marine applications is an easy jump.

Most modern outboard engine and sterndrive-based alternators will push electrons back into a lithium-ion battery bank, although if putting the battery on a trickle charger once you’re back at home or in the marina is a habit, best stick to it.

Modern lithium-ion batteries will also happily hook up to a normal 12-volt charger, with the onboard electronics built into the battery managing how the electrons are stored on board and preventing overcharging.

Yes. First of all, a lithium-ion battery won’t grumble and grouch like a lead-acid battery when it dies, and will instead just stop working. Where the lights will dim as a lead-acid battery loses charge, a lithium-ion equivalent will keep the lights burning bright until the moment it shuts down.

That could be catastrophic for someone who is suddenly stuck offshore with no way of cranking their engine.

That means it’s wise to install a battery monitor on your lithium-ion system to flag if there are any problems.

A battery monitor will check the voltage across the battery system to indicate the state of charge. Better systems will include the rate of discharge and even an estimated battery runtime.

To help boaters manage, some are even being built with Bluetooth connections so that they can be checked and managed via a smartphone app.

Lithium-ion batteries also don’t like extreme cold, but all you need to do is turn on a couple of accessories and the batteries will warm themselves up as they discharge. This will be a rare thing in Australia’s climate.

Also, depending on the age of your boat, a lithium-ion battery system may need some extra tweaking to make it compatible with an order electrical system. The key here is it may be the right time to overhaul your boat's electronics to suit the new system.

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