Lithium vs AGM Batteries for Yachts
7 min read · Updated
Lithium is now the default choice for new-build superyacht house banks — but AGM still has a legitimate role in the right application. The right comparison isn't purchase price; it's usable energy per cycle over the life of the installation.
Usable capacity
AGM is typically limited to 50% depth-of-discharge for reasonable life. Lithium (LiFePO4) is comfortable at 80% DoD. A 1000 Ah AGM bank therefore delivers roughly the same usable energy as a 625 Ah LiFePO4 bank — before considering charge acceptance.
Cycle life and total cost
LiFePO4 delivers thousands of cycles at 80% DoD. AGM delivers hundreds at 50% DoD. Amortised across the life of the vessel, lithium is almost always cheaper per usable kWh — provided the install is done properly.
When AGM still fits
Engine-start banks, short-refit interim solutions, and vessels with tight budgets and limited electrical demand still make sense on AGM. The mistake is running an AGM philosophy on a lithium bank — or vice versa.
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