Marine Battery Calculator
Calculate battery requirements for boats, yachts, sailboats, and marine applications with deep cycle, starting, and house battery sizing
Electrical Loads
Navigation & Safety
Comfort & Convenience
Starting Battery Requirements
Charging System Design
Engine Alternator
Solar Panels
Shore Power
How to Use the Marine Battery Calculator
Select Vessel Type
Choose your vessel type and size. Different boat types have varying electrical requirements and space constraints that affect battery selection and sizing.
Calculate Electrical Loads
Enter the power consumption and daily usage hours for all electrical equipment. Include navigation, safety, comfort, and convenience loads for accurate sizing.
Define Autonomy Requirements
Specify how many days you need to operate without charging. Offshore cruising requires more autonomy than coastal or weekend sailing.
Choose Battery Technology
Select appropriate battery technology based on your budget, maintenance preferences, and performance requirements. Consider weight and space constraints.
Frequently Asked Questions
What's the difference between starting and house batteries on a boat?
Starting batteries are designed to deliver high current for short periods to start engines, while house batteries provide steady power for extended periods to run electronics, lights, and appliances. Starting batteries have thin plates for maximum surface area, while deep cycle house batteries have thick plates for durability during repeated discharge cycles.
How do I choose between AGM, gel, and lithium batteries for marine use?
AGM batteries offer good performance and are maintenance-free with reasonable cost. Gel batteries handle deep discharge better and work well in hot climates but charge slower. Lithium batteries provide the best performance with 50% weight savings, faster charging, and longer lifespan, but cost 3-4 times more initially. Consider your budget, weight constraints, and charging capabilities when choosing.
How much battery capacity do I need for offshore cruising?
Offshore cruising typically requires 3-7 days of autonomy depending on your route and weather windows. Calculate your daily amp-hour consumption and multiply by desired autonomy days, then divide by your battery's usable capacity (50% for lead-acid, 80% for lithium). Most offshore cruisers need 400-800Ah of house battery capacity, with larger vessels requiring more for refrigeration, watermakers, and electronics.
What charging sources should I consider for my marine electrical system?
Primary charging sources include engine alternator (most reliable), solar panels (silent and maintenance-free), wind generator (works day and night), and shore power charger (fastest charging). Many cruisers use a combination: alternator for daily charging while motoring, solar for maintaining batteries at anchor, and shore power when available. Size your alternator to provide 10-25% of battery capacity in amps for efficient charging.
How do I prevent battery problems in marine environments?
Marine battery problems stem from corrosion, vibration, and improper charging. Use marine-grade batteries with robust construction, secure mounting to prevent vibration damage, and apply corrosion protection to terminals. Install proper ventilation for flooded batteries, use a quality battery monitor to track state of charge, and implement temperature compensation for charging. Regular maintenance includes checking connections, cleaning terminals, and equalizing flooded batteries monthly.