Marine Battery Types Explained: Flooded vs AGM vs Lithium (LiFePO4)
Starting vs deep-cycle
Starting batteries deliver big current for a few seconds (CCA/MCA). Deep-cycle house batteries deliver steady current for hours. Dual-purpose batteries compromise on both, which is fine for small boats with one battery.
The three chemistries
| Flooded | AGM | LiFePO4 | |
|---|---|---|---|
| Usable capacity | ~50% | ~50% | 80–90% |
| Cycle life | 300–500 | 400–700 | 3,000–6,000 |
| Weight (100 Ah) | ~60 lb | ~65 lb | ~25–30 lb |
| Maintenance | Water checks | None | None, has a BMS |
| Charging | Standard | AGM profile | Lithium profile, protect the alternator |
When lithium pays off
If you cycle the house bank daily (liveaboards, cruisers, boats with fridges or inverters), LiFePO4's cycle life and usable capacity make it cheaper per kWh over its life. A weekend boat that stays on shore power may not see the payback.
- Victron Lithium Battery Superpack 12V/100AH NG $947.38
- Victron Lithium Battery Superpack 12V/200AH NG $1,808.62
- Xantrex 105AH 12V (Group 27) LIFEPO4 Lithium Battery $497.30
Charge it correctly
Match the charger profile to the chemistry, and fit a shunt-based battery monitor. Voltage alone can't tell you the state of charge on lithium.
- Guest 10A On-Board Battery Charger 12/24V 2 Bank $177.71
- Dual Pro PS2 Auto 15A 2 Bank Lithium/AGM Battery Charger $447.56
- Victron Smartshunt 500A/50MV IP65 Bluetooth Battery Monitor $125.40
- Victron Orion XS 12/12-50A DC-DC Battery Charger $332.44
Shop batteries, battery chargers and battery management.
FAQ
Can I drop a lithium battery in place of my AGM?
Physically, often yes. Electrically, check that your charger, alternator regulation and solar controller have a LiFePO4 profile, and protect the alternator with a DC-DC charger or a regulator built for lithium.
How much usable capacity does each type have?
Plan on about 50% for flooded and AGM to preserve cycle life, and 80–90% for LiFePO4. A 100 Ah lithium gives roughly the usable energy of a 200 Ah AGM bank.
Do I still need a starting battery with lithium?
Most installs keep a separate lead-acid or dedicated starting battery for the engine and use lithium for the house bank.