Let’s talk about a problem that trips up a lot of people. You install a new backup power system, everything looks good—the lithium battery is at 100%, the inverter is a solid brand, the specs match. Then you go to test it under a real load, and… click. The whole system shuts down. You’ve got a full battery, but zero power.
That’s not a faulty part. It’s a design mistake. We see it constantly out in the field, and it’s always the same frustrating issue: the battery and the inverter are not properly matched. Get this one thing wrong, and you’re signing up for chronic underperformance, nuisance shutdowns, and you could even be damaging your components.
This guide is about the simple math to prevent that. We’re just focused on the one calculation you need to build a power system that actually performs under pressure.
12v 100ah lifepo4 battery
Chapter 1: The Core Metrics That Truly Matter
To build a system that works, you have to know what the specs actually mean. Forget the brochure for a second—let’s talk engineering.
1.1 Decoding Your Battery’s Power: Beyond Amp-Hours
The numbers on the label are easy to find. The ones that actually matter for this problem are often in the fine print.
- Voltage (V) & Capacity (Ah): This is level one. Voltage is the system’s electrical pressure. Amp-hours (Ah) is the size of your energy reserve. A 100Ah battery can, in theory, deliver 100 amps for an hour. Fine.
- The REAL King: Continuous Discharge Current (Amps): Pay attention here, because this is everything. This single number determines if your inverter will work or not. It’s the maximum current the battery’s internal Battery Management System (BMS) will allow you to draw without cutting you off. Your Ah capacity is how much fuel is in the tank; the Continuous Discharge Current is the diameter of the fuel line. A giant tank is useless if the line can’t deliver the flow.
- Peak Discharge Current: A short, seconds-long burst of high current. You need this for starting tough loads—think motors, pumps—things with a big initial power draw.
1.2 Decoding Your Inverter’s Thirst: Beyond Watts
The inverter’s job is converting the battery’s DC into usable AC for your equipment.
- Continuous Power (Watts): This is the power an inverter can produce all day long without melting. It’s the big number on the box (e.g., 2000W).
- Surge/Peak Power (Watts): Just like the battery’s peak current, this is a temporary power boost to get demanding appliances started.
- Input Voltage Range: This is a hard rule. The inverter’s voltage must match the battery system’s nominal voltage. 12V, 24V, 48V—they have to be the same. You can’t run a 12V battery on a 48V inverter. Forget it.
If you only learn one thing from this page, this needs to be it.
The simple, non-negotiable rule: Your battery Continuous Discharge Current (Amps) must be GREATER than your inverter maximum current draw (Amps).
To figure out what your inverter is going to demand from the battery, the math is simple:Inverter Current Draw (Amps) = Inverter Power (Watts) / Battery Voltage (V)
Let’s run the numbers for a 1000-watt inverter on a 12V system: 1000W / 12.8V (a typical, real-world LiFePO4 voltage) = 78.1 Amps So, your battery’s BMS rating must be higher than 78.1A. That’s the bottom line.
Let’s apply this to the two situations we get asked about every single week.
3.1 Case Study: Can a 100Ah Battery run a 2000W Inverter?
A classic mismatch. The math tells you everything you need to know.
- Calculation: 2000W / 12.8V = 156.25 Amps
- Analysis: Okay, so the inverter is going to demand 156 amps. Now, go look at the spec sheet for a standard 100Ah LiFePO4 battery. You’ll be lucky to find one with more than a 100A continuous discharge BMS. Since the battery’s safety system (the BMS) has a hard limit of 100A, it will shut down the instant the inverter tries to pull more. So, no. It’s not going to work.
- The Solution: How do you fix it? For that 2000W inverter, you need a battery setup that can happily deliver over 157A without breaking a sweat. That gives you two main options: a single, high-output battery pack like our Titan-Series 200Ah battery (with a 200A BMS), or wiring two of our standard 100Ah batteries in parallel.
3.2 Case Study: What Size Inverter for a 200Ah Battery?
Let’s flip the problem. You already have a battery, what can you run with it?
- The Reverse Calculation: Let’s say you’ve got our Titan-Series 200Ah battery and its 200A continuous BMS.
- Formula: Max Inverter Size (Watts) = BMS Continuous Amps * Battery Voltage
- Calculation: 200A 12.8V = 2560 Watts
- Conclusion: With that battery, you can run a 2500W inverter with a healthy safety margin. Its high cycle life and incredibly flat voltage curve mean it’s a solid foundation for a powerful system.
Chapter 4: The Chemistry Difference: Why LiFePO4 Excels (vs. AGM)
People ask, “Why can’t I just use a 100Ah AGM battery?” The answer comes down to chemistry.
Old lead-acid and AGM batteries suffer from something called the Peukert effect and massive voltage sag. The moment you hit them with a heavy inverter load, their voltage collapses. As the voltage drops, their usable capacity disappears. That 100Ah AGM trying to power a 1500W inverter? It might only give you half its rated capacity before the voltage drops too low and the inverter shuts itself off.
This is where Lithium Iron Phosphate (LiFePO4) is fundamentally better. A good LiFePO4 battery has a nearly flat discharge curve. It holds a stable, high voltage even when you’re pulling a huge load. Remember that 156A load we calculated? A correctly sized LiFePO4 pack will deliver that current from 100% all the way down to empty without its voltage giving up. This reliability is precisely why every serious industrial and commercial application has moved to LiFePO4.
Chapter 5: Quick Reference Sizing Chart
Here’s a quick reference chart for a 12V system. Treat this as a guide, but always—always—check the official datasheet for your specific battery.
| Your Inverter Size (Continuous Watts) | Minimum Required Battery BMS (Continuous Amps) | Our Recommended LiFePO4 Solution |
|---|
| 1000W | ~80A | 1x 100Ah Standard Battery |
| 2000W | ~160A | 1x 200Ah High-Performance or 2x 100Ah Parallel |
| 3000W | ~240A | 1x 300Ah High-Performance or 3x 100Ah Parallel |
Conclusion
Building a good power system is about math, not wishful thinking. Before you buy any components, remember the one thing that matters: your battery’s continuous discharge rating in amps must be higher than your inverter’s maximum draw. It really is that simple. Get that one number right, and you’ll build a system that works.
Ready to build a system that won’t let you down? Browse our full range of high-performance LiFePO4 batteries or Contact kamada power our engineering team for a free system design consultation. We’ll help you spec the perfect pairing for your application.
FAQ
1. What size battery do I need for a 3000-watt inverter?
Simple: a 3000W inverter on a 12V system will pull about 235A (3000W / 12.8V). You need a battery bank that can continuously supply more than that. That usually means a single 300Ah battery with a high-output BMS, or three 100Ah batteries in parallel.
2. Why does my inverter shut off even with a fully charged battery?
The inverter is demanding more amps than the battery’s BMS is willing to give. The BMS is doing its job, which is to protect the cells from being damaged. You either need a battery with a higher continuous discharge rating or a smaller inverter.
3. Can I use a bigger inverter than my battery can technically handle?
Don’t do it. It’s a recipe for headaches. You’d have to constantly worry about your loads not exceeding the battery’s amp limit, which guarantees you’ll get nuisance shutdowns. The right way is to size the battery to handle the inverter’s full continuous rating.
4. How does temperature affect my battery and inverter pairing?
Temperature absolutely matters. LiFePO4 is much better than lead-acid, but extreme cold can still limit its ability to deliver high current. Plus, any good BMS will stop you from charging below freezing to protect the cells. You have to read the datasheets for both components, especially if the system isn’t going in a climate-controlled space.