RV Solar Calc

RV Battery Runtime Calculator: How Long Does a 100Ah Battery Last?

• • 11 min read

The most common question in every RV forum is: "How long will my 100Ah battery last?" The answer depends on your real amp-hour consumption, depth of discharge, inverter efficiency loss, and whether you're running a 12V or 24V system.

Why RV Battery Runtime Calculator Knowledge Matters

Knowing how to use an RV battery runtime calculator correctly is the difference between waking up to a dead battery at 3 a.m. and sleeping soundly. Most RVers never run an actual watt-hour calculation before buying.

Key Insight: A 100Ah lithium LiFePO4 runtime is typically 60–80% longer than a 100Ah AGM under identical loads — because lithium gives you 80–100% of its rated capacity, while AGM safely delivers only 50%.

Step-by-Step RV Battery Runtime Calculator Guide

Step 1 — Do Your Watt-Hour Calculation

Start by finding out how many watt-hours your 100Ah battery actually stores:

Capacity (Ah) × Voltage (V) = Watt-Hours
100Ah × 12V = 1,200 Wh

Apply your depth-of-discharge (DoD) limit to get usable watt-hours:

AGM: 1,200Wh × 0.50 = 600Wh usable
Lithium: 1,200Wh × 0.90 = 1,080Wh usable

Step 2 — Calculate Your Load

List your appliances and their wattage. Divide by 12V to get amp draw:

Example: 600W total load ÷ 12V = 50A draw

Step 3 — Factor in Inverter Efficiency

Inverters waste 5-15% as heat. Divide your AC load by efficiency:

600W ÷ 0.88 (88% efficiency) = 680W total draw

Step 4 — Calculate Runtime

Runtime = Usable Wh ÷ Actual Load (W)
600Wh ÷ 680W = 0.88 hours (53 minutes) with AGM

Lithium vs AGM Runtime Comparison

LoadAGM (50% DoD)Lithium (90% DoD)
100W (8.3A)6-7 hours11-12 hours
200W (16.6A)3-3.5 hours5.5-6 hours
400W (33A)1.5-1.8 hours2.7-3 hours

Calculate Your Exact Runtime

Use our interactive calculator to get precise runtime based on your specific appliances and battery type.

Open the Calculator