How To Properly Size A Battery Bank For Your Boat! PYS Tech Talk
18 June 2026 · 6 min · 4K views
Sailboat at anchor with solar panels and generator visible
What this video covers
Sizing a house battery bank starts with calculating daily amp-hour consumption, and a battery monitor is the most reliable way to get that number — more accurate than online calculators, which frequently over- or undershoot when given imprecise inputs.1:13 The second variable is how many days the boat will sit at anchor without recharging; a crew planning three days on the hook needs a larger reserve than one that moves daily or runs solar and a generator.2:04 Battery chemistry determines usable capacity: flooded lead-acid delivers roughly 35% of rated capacity, AGM about 50%, and lithium about 80%.2:57 Golf-cart batteries illustrate the point — each type rates around 200 amp-hours at 12 volts, but usable output ranges from 70 Ah (flooded) to 160 Ah (lithium), meaning fewer lithium cells can replace a larger lead-acid bank.3:18 Practical bank sizes range from 200 Ah for modest 12-volt systems to 2,000 Ah for heavy lithium installations.4:54 High-draw loads such as refrigeration and air conditioning must be factored in.4:43 Oversizing wastes money; undersizing causes chronic undercharge and forces late-night engine runs to recover voltage.5:12
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