Battery Systems & Lithium Installation

The lithium revolution has reached cruising boats. LiFePO4 (lithium iron phosphate) batteries deliver significantly more usable capacity per kg and per dollar over a 10-year life than AGM. Most cruiser refits now include or plan a lithium retrofit. This guide covers the components, the cost, and where to get it done.

Lithium retrofit components

LiFePO4 cells / drop-in batteries: Battle Born, Victron, Renogy, Epoch, others. 100 Ah blocks common.
BMS (battery management): Built-in (drop-ins) or external (cell-level). Critical for safety.
Lithium-profile chargers: Shore charger, solar controller, alternator regulator.
DC-DC converter or alternator protection: Prevents alternator overload from lithium's high charge acceptance.
Battery monitor: Victron BMV-712, SmartShunt, or equivalent.
Wiring upgrade: Larger conductors for higher current capability.
Class T fuses: Safety-critical for lithium.

What it costs

Component	Common range (USD)	Notes
400 Ah LiFePO4 bank (parts)	$2,800–5,500	4×100Ah drop-ins
600 Ah LiFePO4 bank	$4,000–8,000	6×100Ah
Lithium-profile shore charger	$700–1,400	Victron Multiplus or similar
Alternator regulator (Wakespeed/Balmar)	$500–900	External
Solar charge controller	$200–600	Lithium-capable
Battery monitor + shunt	$200–400	Victron BMV-712 / SmartShunt
Class T fuse + holder (per bank)	$80–200	Safety-critical
Pro installation labour	$2,000–5,000	40-foot boat
Total turnkey lithium retrofit	$8,000–13,000	Mid-range 400–600Ah

Frequently asked questions

Lithium vs AGM?

Lithium: half the weight, double usable capacity, 5x faster charge. Pays back in 5–8 years.

Retrofit cost?

DIY $4,000–8,000 parts. Turnkey $8,000–13,000.

Bank size?

Typical 40-foot cruising boat: 300–500 Ah LiFePO4. More for watermaker, air con.

Charging?

Lithium-profile chargers + alternator regulation or DC-DC.

Where installed?

Annapolis, Fort Lauderdale, San Diego, La Paz, Auckland have specialists. DIY increasingly common.