The Project: Lagoon 45 Lithium Conversion
This is one of the most rewarding installations we've completed — a full house bank lithium conversion on a Lagoon 45 catamaran used for extended bluewater cruising.
The owners had been living aboard for three years with a 600Ah AGM house bank. Despite the large bank, they were constantly managing power: limiting fridge temperature on cloudy days, rationing watermaker use, and running the generator more than they wanted to.
The brief: switch to lithium, keep the same footprint, run the watermaker from solar without generator support.
The Problem with 600Ah of AGM
Six hundred amp-hours sounds like a lot. But in practice, the owners were working with about 300Ah usable (50% depth of discharge limit for AGM longevity).
Their daily loads:
- 100L/day watermaker: ~25A × 2 hours = 50Ah
- 2× refrigerators: ~8A average = 192Ah/day
- Navigation electronics: ~10A × 24hrs = 240Ah/day (on passage)
- Lighting, devices, autopilot: ~30Ah/day (coastal)
At anchor: ~270Ah/day. Available: 300Ah. Margin: 30Ah — almost nothing.
The Solution: 400Ah LiFePO4
We installed four Revolution Power 12V 100Ah batteries in a 2P2S configuration (two pairs in series, then in parallel) — providing 24V/200Ah. Combined with the existing 24V wiring, this gave 200Ah of lithium at 24V — with 190Ah usable versus the 150Ah usable from the original setup.
Wait — that's less capacity on paper. Why does it work better?
Because LiFePO4 accepts charge at a much higher rate. The catamaran's 600W of solar (at 24V) was previously limited by AGM's charge acceptance — the batteries would be at 80% charge by noon and not accepting significant current. The remaining solar was wasted.
LiFePO4 accepts full current until 95% charged. The solar was now useful all day. Net result: more energy harvested, more energy available.
Charging System Changes
Three key modifications:
1. Solar MPPT Controller
Replaced the existing PWM controllers with Victron SmartSolar MPPT 150/70 — set to 24V LiFePO4 profile. This alone increased solar harvest by ~25% through true MPPT tracking versus PWM.
2. Alternator Isolation
Installed 2× Victron Orion-Tr Smart 24/24/17A (one per engine) — isolating the lithium house bank from the two Yanmar alternators. Engine charging now contributes without risk to the alternators.
3. AC Charger Update
The existing Mastervolt Mass Combi charger/inverter was compatible with lithium — we only needed to update the charge profile in its settings.
Results After 6 Months
The owners reported back after their first Caribbean season:
- Generator usage dropped by ~80% — from daily 2-hour runs to once per week on cloudy passages
- Watermaker runs freely — no longer rationed, running during peak solar hours
- Fridge temperatures consistent — no more compromises
- Battery weight reduced by ~40kg across both hulls
- Zero battery maintenance — no equalization charges, no terminal cleaning
The lithium conversion cost approximately $4,800 in batteries plus $2,200 in system upgrades. The AGM bank would have needed replacement within 12 months at ~$2,800. The lithium bank will last 10–15 years.
Planning a Sailboat Conversion?
Every yacht is different — charging sources, loads, battery location, and budget all factor in. Contact our marine team with your boat details and we'll design a conversion plan.