When does a lithium conversion make sense?

These days I keep hearing the same question on board: "Marco, should I switch to lithium?" My answer always starts with a counter-question: how do you cruise, where do you moor, and what is your power consumption? Lithium is fantastic for the right cruising profile, and a waste of money for the wrong one.

In this piece I explain when a conversion from lead-acid (or AGM/gel) to LiFePO4 is worthwhile, and when I advise you to keep what you have. Not a technical treatise. Rather the checklist I run through on board before we even start talking about quotes.

Where lithium really makes a difference

The four practical benefits that drive every conversion:

Property	Lead-acid / AGM	LiFePO4
Usable capacity	~50%	90–95%
Cycle life	±500	3,000+
Weight per Ah	~3× heavier	1×
Full charge time	8–10 hours	2–3 hours

On paper this looks obvious. In practice the implication is bigger: a 200Ah lithium pack behaves like a 400Ah lead-acid pack because you can use almost all of it. Plus you charge half as often, charge faster, and the installation lasts six times longer. That is the real argument.

Who benefits from it

Four cruising profiles where I almost always say "yes":

1. The stay-in-one-place cruiser

Do you regularly anchor for days or weeks, moor at a municipal mooring, or lie at a quiet spot on the Frisian lakes without shore power? You discharge heavily every evening: fridge, lighting, possibly an inverter for 230V. With lead-acid that means charging every morning or running a generator. With lithium you can manage two or three nights without recharging, and when you charge it is done within three hours.

2. The high-consumption owner

Inverter for 230V appliances, microwave, coffee machine, air conditioning, ice maker, watermaker, electric hob: modern yacht comfort needs serious power. Lead-acid can handle this, but you almost always need to run a generator. Lithium makes quiet, clean cruising days possible where the generator only kicks in for charging, not for direct use.

3. The whisper-quiet or electric cruiser

For launches or yachts with (partly) electric propulsion, lithium is practically mandatory. The cycle life of lead-acid simply will not sustain such an installation. Within two seasons you face a replacement. The 2024 project where a launch was fully converted to whisper-quiet electric propulsion would not have been viable without LiFePO4.

4. The weight- and space-optimiser

On a speedboat or smaller cruiser an extra 50 kg of batteries matters. Lithium delivers the same usable capacity in a third of the weight and half the volume. For planing boats where weight distribution affects performance, that is a tangible advantage.

When I advise sticking with lead-acid

Three scenarios where I honestly say a conversion is not a sensible investment:

• The shore-power cruiser. Are you on shore power 90% of the time and does the boat mainly go out for a couple of hours on a Saturday afternoon? You almost never discharge heavily. A good AGM lasts ten years and costs a fraction. For this profile lithium is overkill.
• The boat will be sold within 5 years. A lithium pack only pays for itself over several years of use. If you sell sooner, you rarely recoup that money. Buyers seldom pay extra for the installation.
• Limited budget and an old charger/inverter. An honest lithium conversion often means a new charger and possibly a new inverter as well. If those components need to keep going for years anyway, it is smarter to first replace them with lithium-compatible versions and then do the battery conversion in a few years.

The questions I ask before quoting

When someone calls about a lithium conversion, we first do an onboard consultation. That is not a sales visit. It is gathering information to make a sensible calculation. The questions I always run through:

1. How do you cruise? Nights per year without shore power, average day length, cruising area.
2. What is on board now? Number of batteries, age, type, capacity, 12V or 24V configuration.
3. Which chargers, inverters and alternators are present? Brands, models, age.
4. What is the consumption? Fridge, inverter, navigation, lighting, possibly air conditioning.
5. How old is the wiring between batteries and main loads? Lithium can deliver much higher current peaks. Cables that worked fine for 25 years with lead-acid can fall short.
6. Is there a generator on board? How often does it run? What is the fuel consumption?
7. What are the plans for the boat over the next 5–10 years?

Only with those answers can I tell whether a conversion is sensible, what capacity is needed, whether the existing charger must be replaced, and whether a DC/DC converter is needed between alternator and battery to protect the alternator. Only then does a quote follow.

What makes a good installation

A lithium conversion is more than swapping batteries. The points that separate an installation that lasts ten years from one that fails within two seasons:

• A solid BMS. Not a budget version from AliExpress, but a reliable system with cell balancing, temperature protection and communication with the charging system.
• Adapted charge profiles in the onboard charger, or a charger specifically built for LiFePO4. Lead-acid charge profiles overcharge lithium and shorten its life.
• Alternator protection via a DC/DC converter or an external regulator. Lithium accepts virtually unlimited current. An unprotected alternator burns out.
• Correctly sized cabling and fusing, matched to the higher discharge currents that lithium delivers.
• Integration with shore power and inverter that respects the pack's state of charge rather than ignoring it.

None of these points is rocket science. But one wrong choice in the chain produces an installation that looks fine until the moment you actually load it.