🔹 Quick Answer

Battery Backup Time (Hours) = (Battery Capacity × Voltage × Number of Batteries × Efficiency) ÷ Load (Watts)
Example:
A 100Ah, 48V battery running a 200W load gives ≈ 19.2 hours of backup (assuming 80% usable capacity).

Use this free Battery Backup Runtime Calculator to instantly estimate how long your battery system will power your appliances, inverters, or solar setups — before needing a recharge.

 What Is a Battery Backup Runtime Calculator?

A Battery Backup Runtime Calculator is a tool that helps you estimate how long your battery will last under a specific electrical load.
It’s essential for solar setups, UPS systems, off-grid inverters, RVs, and backup power applications.

By entering:

• Battery Capacity (Ah) – the ampere-hour rating of your battery

• Battery Voltage (V) – usually 12V, 24V, or 48V

• Number of Batteries – connected in your system

• Total Load (Watts) – total power consumption of all devices

…the tool instantly calculates your estimated backup runtime in hours.

Why You Should Use This Tool

✅ Plan your backup power — know how long your inverter or UPS can sustain a given load.
✅ Solar System Sizing — determine how many batteries you need for night usage or cloudy days.
✅ Cost Optimization — avoid over- or under-sizing batteries for your energy storage.
✅ Appliance Protection — ensure your critical devices (routers, CCTV, servers, etc.) stay powered during outages.

Whether you call it a battery backup calculator, battery runtime estimator, or UPS runtime calculator, the goal is the same: know your power duration with confidence.

Formula for Battery Backup Time

The standard formula used by the calculator is:

Where:

• Battery Capacity (Ah) = Amp-hours rating

• Voltage (V) = Battery voltage

• Efficiency = Typically 0.8 (80% usable capacity)

• Load (W) = Power usage of connected devices

Example:

For a 100Ah, 48V system running a 200W load:

So, you’ll get roughly 19 hours of backup before your battery needs recharging.

Real-World Examples

💡 These are approximate values assuming 80% efficiency. Actual results depend on inverter losses, battery age, and temperature.

How to Use the Online Battery Backup Calculator

1. Enter Battery Capacity (Ah) – e.g., 100

2. Enter Battery Voltage (V) – e.g., 48

3. Enter Number of Batteries – e.g., 1

4. Enter Total Load (Watts) – e.g., 200

5. Click 🔌 Calculate Runtime

➡️ Instantly see:

• Total Battery Capacity (Wh)

• Usable Capacity (80%)

• Current Draw (A)

• Estimated Backup Time (Hours)

Example:
Input: 100Ah, 48V, 1 battery, 200W → Output: ≈19.2 hours of runtime

 Applications of This Calculator

• Solar Power Systems: Estimate overnight backup during no-sun hours.

• UPS & Inverters: Calculate how long servers, routers, or computers can run.

• Off-Grid Systems: Plan battery banks for cabins, vans, or tiny homes.

• Battery Design: Compare 12V, 24V, and 48V systems for efficiency.

FAQs

 How do I calculate battery backup manually?

Use the formula:
Backup (hrs) = (Ah × V × No. of Batteries × Efficiency) ÷ Load (W)

 What’s the efficiency of lead-acid vs. lithium batteries?

Lead-acid ≈ 80%, Lithium ≈ 95%. Use 0.8 or 0.95 in calculations accordingly.

How long will a 12V 200Ah battery run a 200W load?

≈ (12×200×0.8)/200 = 9.6 hours.

 Why is my actual backup time less than calculated?

Real-world losses (inverter inefficiency, temperature, battery age) reduce total usable power.

 How often should I re-calculate runtime?

Whenever you add or remove loads, or after 1 year as the battery ages.

 Can I use this for solar batteries?

Yes, it’s ideal for off-grid and hybrid solar systems to estimate nighttime power duration.

 Final Thoughts

A Battery Backup Runtime Calculator is more than a tool — it’s your energy planning companion.
It helps you make smart decisions about:

• Battery sizing

• Load management

• Backup reliability

 Whether you’re designing a home inverter system, running a small solar setup, or managing a data center UPS, this calculator ensures you’re never left guessing.

Try our free Battery Backup Runtime Calculator now and discover exactly how long your power will last.