Lithium batteries on a boat: when they are worth it and when they are not

Switching the house bank of a sailing yacht or a cruising motorboat to lithium (LiFePO4) can be the best electrical upgrade on board… or money you will never get back. It depends on how you use the boat, not on what is fashionable. At Málaga Baterías we supply lithium and AGM batteries for boats in Málaga and along the Costa del Sol, and here we explain plainly when the switch pays off, when it doesn’t and what needs checking on board before you go ahead.

What changes with LiFePO4 compared with AGM

Both technologies work for a house bank. What changes is how much energy you can actually use.

• Usable capacity. An AGM battery should not regularly go much below half its capacity if you want it to last. A LiFePO4 battery lets you use most of its rated capacity as a matter of routine.
• Weight. For the same rated capacity, a lithium battery weighs around half as much as a lead one, or less.
• Cycles. Looked after properly, a LiFePO4 battery withstands several times more charge and discharge cycles than an AGM.
• Charging speed. Lead accepts less and less current as it fills and the last stretch is slow. Lithium takes high current almost to the end and makes better use of engine or sun hours.
• Stable voltage. On an AGM the voltage drops as it discharges. On lithium it stays almost flat to the end.

When switching to lithium pays off

• You anchor out often. If you spend nights away from the marina, every usable amp-hour counts, and lithium gives you more autonomy in the same space.
• You have heavy loads. A compressor fridge, autopilot, instruments, lights and an inverter add up fast.
• You charge from solar panels. Lithium takes everything the panels deliver almost until it is full and doesn’t suffer from sitting at half charge for days. We explain it for campervans in leisure battery with a solar panel.
• Weight matters. Cruiser-racers, multihulls, planing motorboats or boats with the batteries far from the centre: shedding tens of kilos is welcome.
• Intensive use. If you live aboard, make long passages or the boat works in charter, the extra cycles pay for themselves.

When it doesn’t pay off

• Day trips with shore power at the berth. You leave in the morning, come back in the afternoon and the shore charger tops the battery up. You hardly cycle it: a properly sized AGM bank is more than enough.
• Low consumption. If all you have on board is lights, a depth sounder, a radio and little else, you won’t make use of the extra capacity.
• A boat used a few weeks a year. Lithium pays for itself by cycling. If the boat spends nearly all year tied up, you are paying for cycles you won’t use. In that case it matters more to look after what you already have: see how to winterise your boat battery.

And if on top of that you have to replace the charger and controller and add a DC-DC charger without the use to justify it, a good AGM bank is the better buy. We sell both, so we’ll tell you either way.

What to check before you switch

A lithium battery doesn’t simply go “where the old one was” without looking at anything else. Go through this with your marine electrician.

Shore charger and solar controller

Both must have a lithium charging profile (LiFePO4) or let you adjust the voltages. A charger designed only for lead may use voltages and stages, such as equalisation, that don’t suit a lithium battery. If yours doesn’t have that profile, it has to be replaced.

Alternator

A lithium battery accepts so much current that it can keep the alternator working flat out for a long time and overheat it. In addition, if the BMS cuts charging abruptly, the alternator can suffer a voltage spike. The usual solution is a DC-DC charger between the starting circuit and the lithium bank, which limits the current and protects the alternator.

BMS, fuses and cable size

The BMS is the electronics that monitors the cells and disconnects the battery if voltage, current or temperature go out of range. Check the maximum current it allows, especially if you have an inverter or a windlass. Lithium can deliver very high currents, so you need a suitable fuse close to the battery and cable sized for the real current.

The starter battery is still lead

The normal approach is to move only the house bank to lithium. The engine still starts from a lead battery, built to deliver the cranking peak. If you’re not sure which one your engine takes, we cover it in the boat and marine battery guide.

Safety: why LiFePO4

“Lithium” is not one single thing. LiFePO4 (lithium iron phosphate) is the most stable chemistry in the family and the one used in boats and caravanning for house banks. That doesn’t remove the need for a correct installation: battery firmly secured, in a dry, ventilated place, with its fuse, cable of the right size and compatible charging equipment.

Lithium boat batteries we have in Málaga

As an Official Varta Distributor we carry the Varta Professional Li-Ion Deep Cycle range, batteries with a nominal 12.8 V, the voltage of a pack of four LiFePO4 cells in series:

• Varta LL50 12.8V 50Ah: the most compact, 6.8 kg.
• Varta LL100 12.8V 100Ah: 12 kg in a 278 × 175 × 190 mm case.
• Varta LL100LT 12.8V 100Ah: LT version, with the same capacity, dimensions and weight as the LL100.
• Varta LL150 12.8V 150Ah: 20 kg, 353 mm long.
• Varta LL150LT 12.8V 150Ah: LT version, with the same capacity, dimensions and weight as the LL150.
• Varta LL200 12.8V 200Ah: the largest capacity in the range, 30 kg.

If you’re unsure between the standard version and the LT, ask us and we’ll send you the manufacturer’s data sheet for your installation. To compare weights: the LL100 weighs 12 kg and the AGM Varta LA105 12V 105Ah 950A weighs 28.53 kg.

If lithium doesn’t pay off for you, the alternative is the Varta Professional Dual Purpose AGM range, which works for both house and starting duty: from the Varta LA95 12V 95Ah 850A up to the Varta LA210 12V 210Ah 1200A. You’ll find every reference in the boat battery catalogue and more detail on the technology in lithium batteries. For other brands, ask for a quote.

Delivery to Costa del Sol marinas

You can collect the battery from the shop (C/ La Orotava, 100, Málaga) or ask us to bring it to you: we offer battery delivery to marinas in Málaga and along the Costa del Sol. It is delivery only: we don’t fit on board, the installation is done by your marine electrician. Ask us about delivery times. To choose the capacity, message us on WhatsApp with what you have now, your loads and how you charge, or call +34 952 31 01 18.