Depth of Discharge (DoD) refers to how much of a battery's total capacity is used before recharging. For lead-acid batteries (Flooded, AGM, Gel), discharging beyond 50% significantly shortens battery lifespan. A 100Ah lead-acid battery effectively gives you only 50Ah of usable capacity. Lithium LiFePO₄ batteries, however, can safely discharge to 80-100% DoD, meaning a 100Ah lithium battery delivers 80-100Ah of usable power — nearly double the real-world capacity in the same form factor.

The formula is: Runtime (hours) = (Battery Voltage × Amp-hours × DoD × Inverter Efficiency) ÷ Total Load Watts. For example, a 12V 100Ah lithium battery with 80% DoD and 90% inverter efficiency provides 864 usable watt-hours. If your appliances draw 200W continuously, you'll get about 4.3 hours. For daily usage patterns, divide the usable watt-hours by your total daily consumption (sum of watts × hours/day for each appliance) to estimate how many days you can go between charges. This calculator automates all these calculations for you.

Lithium LiFePO₄ batteries are superior for RV off-grid camping (boondocking) for several reasons: (1) Higher usable capacity (80-100% DoD vs 50% for lead-acid); (2) Lighter weight (about 1/3 the weight for the same capacity); (3) Faster charging and better charge efficiency (~99% vs ~85%); (4) Longer lifespan (3,000-5,000 cycles vs 300-500 for lead-acid); (5) Consistent voltage output throughout discharge. The main drawback is higher upfront cost, but the long-term value usually justifies it for frequent off-grid use.

An inverter converts 12V DC battery power to 110V/120V AC for household appliances. This conversion isn't 100% efficient — typical inverters operate at 85-95% efficiency. The remaining 5-15% is lost as heat. If your inverter is 90% efficient and your AC appliances need 500W, the battery must supply about 556W (500 ÷ 0.90). That extra 56W is wasted energy that drains your battery faster. For DC-only appliances (like 12V LED lights and refrigerators), no inverter is needed, so efficiency is effectively 100%. Set the inverter efficiency slider to 100% if all your loads are DC.

Practical tips to maximize off-grid battery duration: (1) Switch to LED lighting — LEDs use 80-90% less power than incandescent bulbs; (2) Use 12V DC appliances whenever possible to avoid inverter losses; (3) Limit high-wattage appliances like microwaves and coffee makers to short bursts; (4) Consider a portable solar panel setup to recharge during daylight; (5) Turn off the inverter when not in use — inverters consume power even when idle (phantom load); (6) Use a battery monitor to track real-time consumption; (7) In cold weather, keep batteries warm — lithium batteries lose capacity below freezing, and lead-acid batteries lose about 20% capacity at 32°F.

For a typical weekend (2-3 days) with basic loads — LED lights, water pump, phone charging, and occasional TV/laptop use — a 100Ah lithium battery (or 200Ah lead-acid) is generally sufficient, providing about 800-1000 usable watt-hours. With modest daily consumption (~250-350Wh), this lasts 2-3 days. For more comfort with a 12V refrigerator, fan, and more electronics, consider 200Ah lithium (or 400Ah lead-acid). For air conditioning or electric heating, you'll need substantial battery banks (400Ah+ lithium) plus a generator or shore power, as these draw 1000-1500W continuously and will drain even large batteries in 1-3 hours. Use this calculator with your specific appliances for an accurate estimate.

Amp-hours (Ah) measure battery capacity at a specific voltage — it tells you how many amps a battery can deliver for how many hours. Watt-hours (Wh) is a more universal measure of energy, calculated as Voltage × Amp-hours. For example, a 12V 100Ah battery stores 1,200Wh of energy. The same 100Ah at 24V stores 2,400Wh. Wh is the better unit for comparing batteries of different voltages and for matching against appliance power ratings (which are always in watts). This calculator shows both so you can understand your actual energy budget.

Parallel wiring (positive to positive, negative to negative) keeps voltage the same but adds capacity — two 12V 100Ah batteries in parallel give you 12V at 200Ah (2,400Wh). Series wiring (positive of one to negative of the next) adds voltage but keeps capacity the same — two 12V 100Ah batteries in series give you 24V at 100Ah (also 2,400Wh). Most RVs use 12V systems with batteries in parallel. If upgrading to a 24V or 48V system, you'd wire in series but need compatible inverters and chargers. This calculator's "Parallel Qty" field lets you easily account for multiple parallel batteries.