Lithium vs AGM: Two Years Later
The lithium retrofit story has matured. Cruising boats that converted in 2023–2024 are now two years in. Reports are mostly positive, but with important caveats — particularly around alternator damage, charge profile mismatches, and the cells' sensitivity to heat in tropical climates.
What's holding up well
- Cell capacity (cruisers report 90–95% of original after 2 years of moderate cycling)
- BMS functionality (drop-in batteries with built-in BMS particularly trouble-free)
- Real-world cycle count (most retrofits seeing 300–500 cycles after 2 years)
- Weight savings genuinely felt — boats noticeably more responsive
What's gone wrong (and why)
- Alternator failures: Lithium accepts charge fast — alternators overheat. Cruisers who installed without external alternator regulation or DC-DC isolators commonly killed an alternator within 6 months.
- Charge profile incompatibilities: Old shore chargers set to AGM profile undercharged lithium. Cells gradually drifted out of balance.
- Heat damage: Cells in poorly ventilated engine rooms or sun-baked lockers degraded faster. Cruisers in Mexico and the Caribbean particularly affected.
- BMS confusion: External-BMS installs (not drop-in) had setup complications cruisers underestimated.
What cruisers wish they'd done differently
- Install proper alternator regulation from day one
- Replace shore charger if old (lithium profile required)
- Plan battery box ventilation; avoid hot installations
- Pick drop-in batteries with internal BMS unless they had specific reason for external
- Buffer the bank slightly larger than their daily-need calculation suggested
Would they do it again?
The consistent answer: yes. Weight savings, charging speed, usable capacity all delivered as promised. The dollar payback is real over 7–10 years vs new AGM cycles. The criticisms are about specific implementation rather than the fundamental technology.
What's changed since
- Drop-in lithium prices have come down 15–25%
- Wakespeed and Balmar alternator regulators are now standard, not optional
- Lithium-spec shore chargers (Victron, Mastervolt) widely available
- Cruiser community has shared install patterns broadly
- Insurance underwriters mostly comfortable now (some still ask questions)
Frequently asked questions
Capacity loss after 2 years?
5–10% in normal use. More in heat-damaged installs.
Alternator the issue?
Yes. External regulator essential.
Would you do it again?
Consistent yes from cruisers reporting back.
Heat sensitivity?
Real. Plan ventilation for tropical climates.
Insurance?
Mostly comfortable now. Some ask for install documentation.