Marine battery buying guide

Cranking batteries deliver short, high-current bursts for starting. Deep-cycle batteries repeatedly power trolling motors and house loads. Dual-purpose batteries compromise between the two when space is limited.

• Use the boat maker’s required BCI group size; it defines case dimensions and often terminal placement.
• Flooded lead-acid is economical but needs ventilation and maintenance. AGM is sealed and vibration-resistant. Marine LiFePO4 can offer usable capacity and lower weight, but only with a compatible BMS, charger and alternator strategy.
• For winter storage, fully charge lead-acid, disconnect parasitic loads, keep it dry and maintain it with a compatible charger. Follow the maker’s temperature and state-of-charge instructions for lithium.