Lithium conversion is the most asked-about boat investment of recent years. Done properly it genuinely transforms a boat: far more usable energy for the same weight, fast charging, long life. Done badly it becomes the most expensive and most hazardous installation aboard.
1. Why People Change
| Property | Lead-acid (AGM/gel) | LiFePO4 |
|---|---|---|
| Usable capacity | About half the nominal figure | Most of the nominal figure |
| Weight | Markedly heavier for the same usable energy | Markedly lighter |
| Charge acceptance | Slows as it approaches full | Accepts high current almost to full |
| Cycle life | Limited; falls quickly with deep discharge | Far longer; tolerates deep discharge |
| Sitting partly charged | Sulphates and loses capacity | No problem, and in fact preferred |
| Charging when cold | Slows down | Must not be charged below freezing, permanent damage |
| Initial cost | Low | High |
The charge-acceptance line is the one that changes life aboard: generator or engine running time falls markedly, because the bank keeps taking high current even when it is nearly full.
2. Five Things That Must Change
1. The BMS
The heart of a lithium installation. It balances cells and disconnects on overcharge, over-discharge, overcurrent and temperature. The question to ask: what happens when it disconnects? If the circuit opens while the alternator is under load, the alternator can be damaged. The installation has to be built for that scenario.
2. Alternator and regulator
Lithium will take everything an alternator can give. A standard alternator is not designed to run at that output continuously and overheats. The answer is an external smart regulator with current limiting, temperature monitoring and the right charge profile. Skip this step and the usual outcome is an alternator dead within a season.
3. Chargers and charging sources
Mains charger, solar controller, wind generator and DC-DC converter all need to support a LiFePO4 profile. Charging lithium on a lead-acid profile is both inefficient and a way of triggering the BMS repeatedly.
4. Separating the start battery
Paralleling them directly forces two different chemistries to sit at the same voltage and damages both.
5. Protection and cable
Lithium can deliver very high short-circuit current. The main fuse must have an interrupt rating suited to what the bank can deliver, and must sit as close to the battery terminal as possible. Cable sizing is recalculated for the new current levels, the old section is often inadequate.
3. Installation and Safety
- Temperature: charging below freezing causes permanent damage. Rarely an issue on the Turkish coast, but it matters on a boat standing ashore through winter. The BMS should have low-temperature protection.
- Location: a dry, ventilated, accessible space. The hot part of an engine compartment is not suitable.
- Securing: because lithium is light, it tends to be secured loosely. A battery moving at sea is a serious hazard.
- Access: BMS and main isolator must be reachable in an emergency.
- Fire: LiFePO4 chemistry is markedly more stable than other lithium chemistries. Even so, short-circuit and overcurrent protection are to be taken seriously.
4. What a Survey Examines
| Item | Check |
|---|---|
| System coherence | Are bank, BMS, charging sources and protection matched; was the installation designed as a whole |
| Alternator arrangement | Is there current limiting; is alternator temperature monitored |
| Charge profiles | Are all sources on a lithium profile, or is one still set for lead-acid |
| Main protection | Fuse interrupt rating and distance from the terminal |
| Cable sizing | Adequate for the new currents; any heating at connections (thermal camera) |
| Start battery separation | Is there a DC-DC converter, or is it paralleled directly |
| Location and securing | Dry, ventilated, secure and accessible |
| Documentation | Who installed it, which products, is there a schematic |
5. Who Should, Who Should Not
- Worth it: boats that spend long periods at anchor, carry high refrigeration and electronics loads, want to cut generator hours, or already have solar.
- Usually unnecessary: boats that sit on shore power in a marina and are used for day sailing with low electrical load. A new AGM bank and a decent charger do the same job for far less.
- Be careful: on a boat you intend to sell soon. Most of the investment does not reach the price, particularly if it is undocumented.
Frequently Asked Questions
Related Pages
Tell us your current system and how you use the boat; we will see together whether a conversion makes sense.