Enter your Battery Type, Capacity, Auxiliary Batteries, System Voltage, Total Load Power, and Desired Runtime into the Dual Battery System Calculator to find your Total Usable Capacity, Estimated Runtime, Current Draw, and Recommended Fuse Size.
Total Usable Capacity
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Estimated Runtime
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Current Draw
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Recommended Isolator Rating
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Minimum Wire Gauge
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AGM batteries are more affordable and reliable but can only be discharged to 50% capacity. Lithium batteries cost more but can be discharged to 100%, offering twice the usable capacity and longer lifespan.
Find the power rating on your device's data plate in watts. If only amps are listed, multiply amps by 12V to get watts (e.g., 4A × 12V = 48W). Add up all devices for total consumption.
The isolator should be rated at least 25% higher than your alternator's maximum output current. Most vehicles need a 100-140A isolator, but check your alternator specifications.
No, never mix different battery types (flooded, AGM, gel, lithium) in the same system. They have different charging requirements and will cause premature failure.
Extreme temperatures reduce battery capacity and efficiency. Cold weather below 0°F can reduce capacity by 20-30%, while heat above 85°F shortens battery life significantly.
Wire gauge depends on current draw and distance. Higher current and longer distances require thicker wire. Use 4 AWG for most installations, 2 AWG for high-current applications over 100A.
Runtime depends on battery capacity, number of batteries, and load power. The calculator accounts for safe discharge limits: 50% for lead-acid batteries, 100% for lithium.
Shore power charging is recommended for extended camping or when the vehicle alternator can't fully charge the batteries. It ensures batteries are maintained at optimal charge levels.