Battery Life Calculator
Battery Life Calculator
Calculate how long your deep-cycle battery will run your devices before dying or sustaining permanent damage.
Battery Drain Over Time
Discharge Schedule
| Hours Elapsed | Ah Remaining | Battery % |
|---|---|---|
| 0 hrs | 100 Ah | 100% |
| 1 hrs | 95 Ah | 95% |
| 2 hrs | 90 Ah | 90% |
| 3 hrs | 85 Ah | 85% |
| 4 hrs | 80 Ah | 80% |
| 5 hrs | 75 Ah | 75% |
| 6 hrs | 70 Ah | 70% |
| 7 hrs | 65 Ah | 65% |
| 8 hrs | 60 Ah | 60% |
| 9 hrs | 55 Ah | 55% |
| 10 hrs | 50 Ah | 50% |
| 11 hrs | 45 Ah | 45% |
| 12 hrs | 40 Ah | 40% |
| 13 hrs | 35 Ah | 35% |
| 14 hrs | 30 Ah | 30% |
| 15 hrs | 25 Ah | 25% |
| 16 hrs | 20 Ah | 20% |
| 17 hrs | 15 Ah | 15% |
| 18 hrs | 10 Ah | 10% |
| 19 hrs | 5 Ah | 5% |
| 20 hrs | 0 Ah | 0% |
Understanding Battery Capacity (Amp-Hours)
Whether you are building a solar system for an RV, powering a portable fridge for overlanding, or setting up a trolling motor for a boat, your primary limitation is battery capacity. Deep cycle batteries are measured in Amp-Hours (Ah). This metric tells you exactly how much electrical current the battery can hold. If a device draws 5 Amps of current, and you run it for 2 hours, you have consumed 10 Amp-Hours of battery capacity.
The Lead-Acid 50% Rule
The biggest mistake beginners make is assuming they can use all of the electricity inside their battery. If you own a traditional Lead-Acid battery (which includes Flooded, AGM, and Gel types), you can only use 50% of the battery's rated capacity.
Why? Because of the internal chemistry. If you discharge a Lead-Acid battery below 50%, the chemical reaction inside the battery physically degrades the lead plates. The battery will permanently lose capacity and fail completely within a few months. Therefore, a massive, heavy 100Ah Lead-Acid battery only truly gives you 50Ah of usable power.
Why Lithium (LiFePO4) is the New Standard
In recent years, Lithium Iron Phosphate (LiFePO4) batteries have become the gold standard for off-grid power. Lithium chemistry is vastly superior to Lead-Acid because it does not suffer from deep-discharge damage. You can safely discharge a Lithium battery down to 10% (or even 0%) hundreds of times without hurting the battery.
This means a 100Ah Lithium battery provides 90Ah of usable power—nearly double the usable power of a Lead-Acid battery of the exact same size. Furthermore, Lithium batteries weigh roughly half as much, making them significantly better for RVs and boats where weight is a major concern.
How to Calculate Total Device Draw
If you have multiple devices running at the same time, simply add their Amperages together. For example, if your portable fridge draws 4 Amps, your LED lights draw 1 Amp, and your phone charger draws 2 Amps, your Total Device Draw is 7 Amps. You plug that number into the calculator to see exactly how many hours your system will survive before shutting down.
Frequently Asked Questions
What Is a Battery Life Calculator?
The Battery Life Calculator is a practical online tool designed to give you fast, reliable answers for everyday decisions. Whether you are planning a budget, comparing options, or verifying a quick estimate, this calculator removes the guesswork and delivers clear, actionable numbers. It is built for anyone who needs a dependable result without wading through spreadsheets or manual formulas. By focusing on the inputs that actually matter, the Battery Life Calculator keeps the experience simple while still producing a trustworthy output you can act on with confidence.
How It Works
Using the Battery Life Calculator is straightforward. Enter the key values in the input fields above, adjust any advanced options if they apply to your situation, and click the Calculate button. The calculator applies the standard industry formula behind the scenes and instantly updates every result component on the right, including the primary result card, the three-stat bar, the breakdown table, the chart, and the summary statistics. All inputs are pre-filled with realistic defaults so you see a complete result the moment the page loads. The tool validates your entries and handles edge cases such as zero, negative, or empty values without crashing, so you always get a clean, readable answer rather than an error or a NaN.
Understanding Your Results
The results panel is organized so the most important number is always at the top, followed by supporting metrics that put that number in context. The breakdown table shows exactly how each input contributes to the total, and the chart visualizes the distribution so you can spot the biggest drivers at a glance. Use the summary statistics block to cross-check the headline figure against the detailed rows, because the two are designed to match exactly. Adjust any input and click Calculate again to compare scenarios side by side, which makes the Battery Life Calculator useful for both quick checks and deeper what-if analysis.
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