Whenever someone asks me, “How long will my inverter battery last?” I smile—because this is one of the most common and important questions in the entire power backup industry. Whether you're using an inverter for your home, running a small shop, operating a clinic, or managing a business where downtime means losses, understanding battery backup time calculation is essential.

In this blog, I’ll walk you through the simplest way to calculate battery backup time, explain why backup differs from system to system, and share a complete battery backup time calculation table that you can refer to anytime. I’ll also include insights from my years of experience working with manufacturers, installers, and brands that operate as an online ups manufacturer, online ups supplier, and online ups trader.

Let’s dive in and simplify this once and for all.

Why Battery Backup Time Matters

I’ve met customers who bought big inverters but ended up disappointed simply because they didn’t estimate their backup needs correctly. Backup time helps you:

• Choose the right battery size

• Know what appliances you can run

• Avoid overloading

• Understand when to upgrade

• Plan for power cuts or off-grid systems

Whether you’re a business owner or a homeowner, battery backup is your safety net. The better you understand it, the better your power system performs.

How to Calculate Battery Backup Time 

Before I show you the complete table, let’s understand the formula.

Backup Time (in hours) =
(Battery Voltage × Battery Ah × Battery Efficiency) ÷ Load in Watts

Most batteries have around 80% efficiency, though tubular and lithium batteries may deliver higher real-world performance.

Here’s a quick example:

A 12V 150Ah battery running a 300W load:

Backup = (12 × 150 × 0.8) ÷ 300
Backup = 1440 ÷ 300
Backup = 4.8 hours

This is the simplest form—and the one I personally use during consultations.

Factors That Affect Backup Time

This is where customers often get confused. Two people may have the same battery but different backup times. Why?

1. Battery Age

Older batteries give less backup because plate capacity reduces over time.

2. Battery Type

• Tubular batteries offer longer backup.

• SMF batteries offer shorter backup.

• Lithium batteries deliver the best backup duration.

3. Load Variation

The more appliances you run, the more backup drops.

4. Inverter Efficiency

A good inverter from a reputed online ups manufacturer ensures better real-world results.

5. Depth of Discharge

Some batteries should not be discharged below 60–70%.

These factors may sound technical, but trust me—understanding them improves your system life by years.

Battery Backup Time Calculation Table 

Below is the cleanest, most user-friendly table showing different backups for different loads and battery sizes. I’ve prepared this after years of actual field experience.

 12V Battery Backup Calculation Table

For 12V 100Ah Battery (Efficiency 80%)

Load (Watts)	Backup Time (Hours)
50W	19.2 hrs
100W	9.6 hrs
150W	6.4 hrs
200W	4.8 hrs
300W	3.2 hrs

For 12V 150Ah Battery

Load (Watts)	Backup Time (Hours)
100W	14.4 hrs
200W	7.2 hrs
300W	4.8 hrs
400W	3.6 hrs
500W	2.8 hrs

For 12V 200Ah Battery

Load (Watts)	Backup Time (Hours)
100W	19.2 hrs
200W	9.6 hrs
300W	6.4 hrs
400W	4.8 hrs
500W	3.8 hrs
600W	3.2 hrs

24V Battery Backup Calculation Table (Dual Battery)

For 24V 150Ah Battery

Load (Watts)	Backup Time (Hours)
200W	14.4 hrs
400W	7.2 hrs
600W	4.8 hrs
800W	3.6 hrs
1000W	2.8 hrs

For 24V 200Ah Battery

Load (Watts)	Backup Time (Hours)
300W	12.8 hrs
500W	7.68 hrs
800W	4.8 hrs
1000W	3.84 hrs
1200W	3.2 hrs

 48V Battery Backup Calculation (4-Battery Bank)

48V systems are common in larger inverters like 5kVA, 7.5kVA, or 10kVA models. They offer more efficient power delivery.

For 48V 150Ah Battery Bank

Load (Watts)	Backup Time (Hours)
500W	11.5 hrs
1000W	5.76 hrs
1500W	3.84 hrs
2000W	2.88 hrs
2500W	2.3 hrs

For 48V 200Ah Battery Bank

Load (Watts)	Backup Time (Hours)
500W	15.3 hrs
1000W	7.68 hrs
1500W	5.12 hrs
2000W	3.84 hrs
3000W	2.56 hrs

How to Use This Table for Your Home or Business

Let me share how I guide my own customers:

Step 1: Calculate Your Load

List your appliances and wattage:

• Fans: 60–80W

• LED lights: 9–12W

• TV: 80–150W

• Refrigerator: 150–300W

• AC: 900–1800W (not recommended on a small inverter)

Step 2: Check Battery Voltage & Ah

Most homes use:

• 12V 150Ah

• 12V 200Ah

• 24V 150Ah

Large homes and businesses use:

• 48V 150Ah

• 48V 200Ah

Step 3: Match It With the Table

Once you know your load, just refer to the right table for expected backup.

It truly simplifies the decision-making process.

What I Recommend for Different User Types

For Homeowners

A 12V 150Ah or 12V 200Ah battery gives comfortable backup for fans, lights, and a TV.

For Shops

A 24V 150Ah setup handles billing machines, computers, fans, and lights well.

For Offices

A 48V system is ideal because it handles computers efficiently.

For Clinics & Labs

Use tubular batteries from a reputed online ups manufacturer for longer life.

Why Backup Time Differs Even With the Same Battery

Many customers ask me:
“My neighbor gets 5 hours, why do I get only 3 hours?”

Here are the common reasons:

• Different appliance usage

• Lower battery health

• Lower charging voltage

• Higher surrounding temperature

• More appliances running at the same time

• Inverter efficiency differences

A high-quality inverter from a reliable online ups supplier or online ups trader always delivers better backup.

My Tips to Increase Battery Backup Time

From hands-on field experience, here are practical and effective tips:

• Do not overload the inverter

• Use energy-efficient appliances

• Keep battery terminals clean

• Allow full charging cycles

• Avoid frequent deep discharge

• Keep batteries in cool, ventilated areas

A well-maintained battery can last 5–7 years, especially tubular batteries.

Solar & Battery Backup Time – A Bonus Advantage

If you pair your battery with solar panels, you gain:

• Extended backup

• Faster charging

• Lower grid electricity usage

• Long-term cost savings

Solar inverters from certified online ups manufacturers deliver the best overall efficiency.

Conclusion

Understanding battery backup time is not just about numbers—it’s about making smarter decisions for your home or business. With the calculation method and detailed backup tables I’ve shared, you now have a clear, practical way to plan your load, choose the right battery, and avoid power shortages.

If you're planning to grow your business, supply batteries, or distribute inverter solutions, this is the right time to step into the growing power backup industry.