To size a battery bank for a 5000W inverter, you need a 48V system with an absolute minimum of 150 Amp-hours (Ah) of Lithium iron phosphate (LiFePO4) capacity, though 300Ah to 400Ah is recommended for realistic daily use. At full load, a 5000W inverter pulls roughly 120 to 125 amps from a 48V battery bank. You must ensure your battery's continuous discharge rating (BMS limit) exceeds this 125-amp draw, or the system will shut down instantly when powering heavy loads like air conditioners or well pumps.
A 5000-watt (5kW) inverter is a serious piece of equipment capable of running almost any household appliance. However, an inverter is only as good as the battery bank supplying its power. If you pair a massive 5000W inverter with an undersized battery bank, the system will fail under heavy load, potentially damaging your equipment or creating a fire hazard.
In this comprehensive guide, we will walk you through the math step-by-step to ensure you build a battery bank that can handle the massive power draw of a 5kW inverter safely and efficiently. If you want to skip the math, use our free WattSizing Calculator to size your entire system instantly.
Understanding the Scope: What Can a 5000W Inverter Run?
Before sizing the batteries, it is important to understand what a 5000W inverter actually does. A 5000W inverter can supply 5000 watts of continuous AC power. Most high-quality 5000W inverters also have a surge rating of 10,000 watts for a few seconds to start electric motors (like those found in refrigerators, air conditioners, and well pumps).
With 5000 continuous watts, you can simultaneously run:
- A 1-ton mini-split air conditioner (1000W)
- A full-size refrigerator (400W)
- A microwave oven (1500W)
- A well pump (1200W)
- Lights, laptops, and a TV (400W)
Because the potential power draw is so high, the DC side of the system (the batteries and cables) must be incredibly robust.
Crucial Sizing Factors Often Overlooked
Many basic solar guides simply divide watts by volts and give you an amp-hour recommendation. However, when dealing with a massive 5000W load, several critical engineering realities come into play:
- BMS Discharge Limits: Every lithium battery has a Battery Management System (BMS). A standard 48V 100Ah server rack battery often has a 100-amp continuous discharge limit. Since a 5000W inverter pulls ~125 amps at full load, a single 100Ah battery will instantly shut down to protect itself. You must wire multiple batteries in parallel to share the current load.
- Inverter Inefficiency: Inverters are not 100% efficient at converting DC power to AC power. Most operate at 85% to 90% efficiency. This means to get 5000W of AC power out, the inverter must pull roughly 5800W of DC power from the batteries.
- The Peukert Effect (Lead-Acid Only): If you use lead-acid batteries, discharging them rapidly (like pulling 100+ amps) drastically reduces their total usable capacity. A 400Ah lead-acid bank might only act like a 250Ah bank under a heavy 5000W load.
- Voltage Sag: High amp draws cause battery voltage to temporarily drop. If the voltage sags too low, the inverter's low-voltage disconnect (LVD) will trigger, shutting off your power even if the batteries aren't fully empty.
Step 1: Choose the Right System Voltage (Why 48V is Mandatory)
The first and most critical decision when sizing a battery bank for a 5000W inverter is choosing the system voltage.
While 12-volt systems are common for small RVs and vans, you should never use a 12V battery bank with a 5000W inverter. Here is the math explaining why:
To calculate the amperage your inverter will pull from the batteries, you divide the wattage by the voltage, and factor in an 85% inverter efficiency. Formula: (Watts / Volts) / 0.85 = DC Amps
- At 12 Volts: (5000W / 12V) / 0.85 = 490 Amps
- At 24 Volts: (5000W / 24V) / 0.85 = 245 Amps
- At 48 Volts: (5000W / 48V) / 0.85 = 122.5 Amps
Pulling 490 amps continuously from a 12V system is incredibly dangerous. It requires massive, expensive, and rigid 4/0 AWG cables (often doubled up) to prevent the wires from melting or catching fire. Finding fuses and breakers rated for 500+ amps DC is also difficult and expensive.
At 48 volts, the current drops to a manageable 122.5 amps. You can safely use much thinner, cheaper, and more flexible wiring (like 2 AWG or 1/0 AWG). For a 5000W inverter, a 48V battery bank is the industry standard, though a 24V system is acceptable if wired very carefully with thick cables.
Step 2: Choose Your Battery Chemistry (Lithium vs. Lead-Acid)
The type of battery you choose drastically affects how large your battery bank needs to be. For a 5000W inverter, Lithium Iron Phosphate (LiFePO4) is highly recommended over Lead-Acid (AGM/Gel/Flooded).
Depth of Discharge (DoD)
- Lead-Acid Batteries: You should never discharge a lead-acid battery below 50% capacity to avoid permanent damage. Therefore, a 400Ah lead-acid battery bank only provides 200Ah of usable power.
- Lithium (LiFePO4) Batteries: Lithium batteries can safely be discharged to 80%, 90%, or even 100% of their capacity without damage. A 400Ah lithium battery bank provides 320Ah to 400Ah of usable power.
Discharge Rates (C-Rate)
Lead-acid batteries suffer from severe voltage sag and capacity loss when discharged quickly. Pulling 125 amps from a lead-acid bank will cause the voltage to plummet, potentially triggering the inverter to shut off prematurely. Lithium batteries maintain a steady voltage curve even under extreme loads, making them perfectly suited for high-draw 5000W inverters.
Step 3: Calculate the Required Battery Capacity (Illustrative Example)
Now we need to determine how many Amp-Hours (Ah) your battery bank needs to be. This depends entirely on how much energy you consume daily, not just the maximum wattage of the inverter.
Let's look at an illustrative worked example for an off-grid cabin running a 5000W inverter on a 48V system.
1. Estimate Daily Energy Consumption
First, list the appliances you plan to run and calculate their daily Watt-hours (Wh).
- Refrigerator: 1.5 kWh/day (1500 Wh)
- Lights & Electronics: 1.0 kWh/day (1000 Wh)
- Well Pump (runs 1 hour total): 1.2 kWh/day (1200 Wh)
- Mini-Split AC (runs 4 hours): 4.0 kWh/day (4000 Wh)
- Microwave/Coffee Maker: 0.5 kWh/day (500 Wh)
- Total Daily Usage: 8,200 Wh (8.2 kWh)
2. Convert Watt-Hours to Amp-Hours
Divide the total daily Watt-hours by your system voltage (48V) to find the required Amp-hours.
- 8,200 Wh / 48V = 170.8 Ah per day
3. Factor in Inverter Inefficiency
Multiply by 1.15 to account for the ~15% energy lost during the DC-to-AC conversion.
- 170.8 Ah x 1.15 = 196.4 Ah
4. Factor in Depth of Discharge (DoD) and Autonomy
If you want the batteries to last for one full day of autonomy (no sun/charging) without dropping below a safe 80% Depth of Discharge for Lithium:
- 196.4 Ah / 0.80 = 245.5 Ah
Result: To comfortably power this cabin, you need a 48V Lithium battery bank rated for at least 250 Ah (roughly 12 kWh of storage).
Note: If you wanted 2 days of autonomy (powering the cabin for two days with zero solar input), you would double this to a 500Ah 48V battery bank.
Practical Checklist: What to Do Next
If you are ready to build your 5000W inverter system, follow these practical steps:
- Verify the Inverter Voltage: Ensure you purchase a 48V version of the 5000W inverter. Do not buy a 12V version.
- Check the Battery BMS Rating: If buying 48V server rack batteries (e.g., 48V 100Ah), check the continuous discharge rating. If it is 100A, you must buy at least two and wire them in parallel to safely handle the 125A draw of the inverter.
- Size the Cables: Use pure copper (not Copper Clad Aluminum / CCA). For a 48V 5000W system, 1/0 AWG or 2/0 AWG welding cable is ideal for the run between the battery busbar and the inverter. Keep this cable as short as possible (under 5 feet).
- Install a Class T Fuse: Install a high-quality Class T fuse on the positive cable as close to the battery terminal as possible. For a 125A continuous draw, a 175A or 200A Class T fuse provides a safe margin.
- Use a Calculator: Double-check your specific appliance loads using the WattSizing Calculator.
Frequently Asked Questions (FAQ)
Can I run a 5000W inverter on a 12V battery bank?
While 12V 5000W inverters exist, they are highly discouraged. A 5000W load at 12V pulls nearly 500 amps. This requires massive, expensive 4/0 AWG wiring (often doubled) and generates a tremendous amount of heat, creating a severe fire risk if connections are not perfectly torqued. A 48V system is the safe standard for 5000W inverters.
How many 100Ah batteries do I need for a 5000W inverter?
If you are using 48V 100Ah lithium server rack batteries, you need a minimum of two wired in parallel (creating a 48V 200Ah bank). A single 100Ah battery's BMS is usually limited to 100 amps of continuous discharge, which will trip and shut down when the 5000W inverter attempts to pull its maximum 125 amps.
What size wire do I need between the battery and a 5000W inverter?
For a 48V system pulling ~125 amps, you should use 1/0 AWG or 2/0 AWG pure copper cable, keeping the distance between the batteries and the inverter under 5 feet. For a 24V system pulling ~250 amps, you must use massive 4/0 AWG cable.
What size fuse do I need for a 5000W inverter?
To size the fuse, take the maximum continuous amp draw and multiply by 1.25 (a 25% safety margin). For a 48V system (125 amps max draw): 125A x 1.25 = 156A. You should use a 175A or 200A Class T fuse. Class T fuses are required for lithium batteries because they have the high interrupt rating necessary to stop a massive dead-short current spike.
How long will a 5000W inverter run on a 48V 100Ah battery?
A 48V 100Ah lithium battery holds 4,800 Watt-hours of energy. If you run the inverter at its absolute maximum 5000W capacity, the battery will be dead in roughly 50 minutes (assuming the battery's BMS allows a 100A+ discharge, which many do not). If your average load is only 1000W, the battery would last about 4.5 hours.
