RV Battery Bank Size Calculator

Understanding RV Battery Capacity

If you plan to "boondock" or camp "off-grid" (without plugging into a campground pedestal), your battery bank is the heart of your RV. It powers your lights, water pump, furnace fan, refrigerator control board, and with an inverter, your AC appliances like a microwave or laptop charger.

A battery bank that is too small means waking up freezing cold at 3 AM because the furnace cut off due to low voltage, or worse, permanently damaging your batteries by draining them completely dead.

Amp Hours (Ah) Explained

Battery capacity is measured in Amp Hours. Think of your battery like a water tank; the Amp Hour rating is the total number of gallons the tank holds.

If a TV draws 5 Amps of power, and you watch it for 2 hours, you have consumed 10 Amp Hours (5A x 2h = 10Ah) from your battery "tank." If you have a 100Ah battery, you would theoretically have 90Ah left to run other appliances. However, because of Depth of Discharge rules, you rarely have access to the full "tank."

Depth of Discharge (DOD): The Usable Capacity Trap

Traditional Lead Acid (Flooded & AGM)

To prevent permanent chemical damage and ensure your batteries live for years, traditional heavy lead-acid batteries should never be discharged below 50% capacity. Therefore, a massive 100Ah AGM battery actually only provides 50Ah of usable power before you must start a generator or rely on solar panels to recharge it.

Lithium Iron Phosphate (LiFePO4)

Lithium is the modern gold standard. A lithium battery can be safely drained down to 10% or even 0% (depending on the internal battery management system) hundreds of times without damage. This means a 100Ah lithium battery gives you 80 to 90Ah of usable power. Thus, a single 100Ah lithium battery provides nearly the equivalent usable energy as two heavy 100Ah AGM batteries paired together.

Frequently Asked Questions (FAQ)

Can I mix different sizes or ages of batteries in my bank?

No. Always wire batteries of the exact same capacity, chemistry, brand, and age together. If you wire an old, weak battery in parallel with a brand new, strong battery, the new battery will expend its energy constantly trying to "charge" and support the weak battery, eventually ruining both.

Do I need 12-Volt or 6-Volt batteries?

Many boondockers prefer wiring two 6-volt "golf cart" batteries in series to create a massive 12-volt battery. 6-volt batteries have incredibly thick lead plates designed for deep, heavy discharging, making them far more robust and long-lasting than standard 12-volt "marine deep cycle" batteries sold at auto parts stores. However, if choosing Lithium, standard 12-volt blocks are the modern standard.