By 
A 1,000 W inverter draws about 93 A at full load. This is true for a 12 V system. Therefore, you need a battery that can deliver at least 100 A continuously. A 12 V 100 Ah LiFePO4 battery with a 150 A BMS is the practical minimum. It runs the inverter at full power for about one hour. For longer runtime, you will need more capacity. Also, if you use AGM, plan on 200 Ah or more.
Batteries for an inverter calculator
Estimates use the formulas explained in this guide. Plan a complete system with the all-in-one calculator →
Step 1: Battery current
Battery current = Inverter watts ÷ (Battery voltage × Inverter efficiency)
1,000 ÷ (12 × 0.90) = 93 A
At 24 V, it is 46 A. However, a 1,000 W inverter fits comfortably at 12 V.
Step 2: Make sure the battery can deliver it
- For LiFePO4, check the BMS continuous discharge rating. A 100 A BMS will run a 1,000 W inverter at full load. This is right at its limit. It may trip on motor surges. A 150 A or 200 A BMS is better. You can also use two 100 Ah batteries in parallel. See battery C-rating.
- A single 100 Ah AGM battery sags hard at 93 A. Its voltage can drop below the inverter’s low-voltage cutoff. This happens long before the battery is half empty. Therefore, two or more batteries in parallel will spread the load. See inverter low voltage cutoff.
Step 3: Size for runtime
Runtime (hours) = Usable Wh × 0.90 ÷ Load watts
| Battery (12 V) | Usable Wh | 1,000 W load | 500 W load | 250 W load |
|---|---|---|---|---|
| 100 Ah LiFePO4 | 1,088 | about 1 hour | 2 hours | 3.9 hours |
| 200 Ah LiFePO4 | 2,176 | 2 hours | 3.9 hours | 7.8 hours |
| 100 Ah AGM | 600 | under 30 min* | about 1 hour* | 2.2 hours |
| 200 Ah AGM | 1,200 | about 1 hour* | 2.2 hours | 4.3 hours |
*AGM delivers less than its rated capacity at high currents (Peukert effect), so expect shorter times at heavy loads.
Most people do not continuously run a 1,000 W inverter at full power. So, calculate your real loads with the load calculation worksheet.
Cables and fuse
This applies to a 1,000 W, 12 V inverter. It also assumes a short run. This means under 1.5 meters each way.
- Cable: 4 AWG minimum, 2 AWG preferred (about 25 to 35 mm²).
- Fuse: about 125 to 150 A, as close to the battery positive as possible, following the inverter manual.
Undersized cables cause voltage drop. As a result, this triggers low-voltage alarms even with a full battery. See battery cable and fuse size.
What a 1,000 W inverter runs
Laptops, TVs, lights, fans, a small fridge (check surge), a blender, a small coffee maker (often 600 to 900 W), CPAP machines and power tool chargers. Microwaves usually draw 1,200 to 1,600 W from the outlet even when labelled “700 W” or “1,000 W” cooking power, so many will not run. See microwave on an inverter.
Recharging with solar
Replacing 1,088 Wh per day at 4.5 peak sun hours needs about 300 W of panels. See what size solar panel to charge a 12 V battery.
Use the solar calculator to size the battery for your total daily use.
Worked example: a weekend camper with a 1,000 W inverter
Loads through the inverter: laptop (60 W, 4 h), TV (60 W, 3 h), coffee maker (700 W, 10 min), blender (400 W, 5 min), phone chargers (20 W, 3 h). The 12 V fridge, lights and fan run on DC.
| Load | Energy |
|---|---|
| Laptop | 240 Wh |
| TV | 180 Wh |
| Coffee maker | 117 Wh |
| Blender | 33 Wh |
| Phone chargers | 60 Wh |
| AC subtotal ÷ 0.90 inverter | 700 Wh |
| DC loads (fridge, lights, fan) | 450 Wh |
| Daily total from the battery | about 1,150 Wh |
A single 12 V 100 Ah LiFePO4 battery offers about 1,090 Wh of usable power. This is just short for a full day without solar. However, a 200 Ah battery is comfortable. You can also use a 100 Ah battery with 300 W of solar. The coffee maker draws 700 W, or about 65 A. This is fine for a 100 A BMS battery.
Battery choices for a 1,000 W inverter
| Battery | Runs 1,000 W at full load? | Typical runtime at a 300 W average |
|---|---|---|
| 12 V 100 Ah LiFePO4, 100 A BMS | Only just (93 A) | about 3.3 hours |
| 12 V 100 Ah LiFePO4, 200 A BMS | Yes | about 3.3 hours |
| 12 V 200 Ah LiFePO4 | Yes | about 6.5 hours |
| 2 × 12 V 100 Ah AGM in parallel | Yes, with voltage sag | about 3.2 hours |
Installation tips
- Keep inverter cables under about 1.5 m each way at 12 V.
- Mount the inverter where it can breathe; heat triggers derating.
- Use the inverter’s remote switch or search mode to cut idle draw when you are not using AC.
- Place the main fuse within about 18 cm of the battery positive.
Common mistakes
- Using your inverter for DC-capable loads. You will waste 10 to 20% when you run a 12 V fridge through an inverter.
- Buying a 1,000 W “modified sine” inverter for a CPAP, laptop or fridge. Use pure sine.
- Ignoring surge: A 1,000 W inverter may not start a household fridge. This is especially true if other loads are running.
FAQ
Can I run a 1,000 W inverter from a car battery?
A starter battery handles small loads. You should use it with the engine running. This battery type is not for deep discharge. Therefore, repeated cycling will damage it.
How many batteries for a 1,000 W inverter?
One 12 V 100 Ah lithium battery with a high-current BMS is the minimum; two give comfortable runtime and current headroom. With AGM, use at least two 100 Ah batteries.
Will a 1,000 W inverter drain my battery when nothing is plugged in?
Yes, slowly. Idle draw is typically 8 to 20 W, which is 0.2 to 0.5 kWh per day. See inverter idle power draw.
Can a 50 Ah battery run a 1,000 W inverter?
You can use it only briefly. Also, its BMS must allow 100 A. This is rare for 50 Ah batteries. Therefore, use 100 Ah or more.
How long will a 1,000 W inverter run on a 200 Ah battery?
A LiFePO4 battery lasts about 2 hours at a full 1,000 W load. However, at a 250 W average, you will get about 8 hours.
Related guides
- How Many Batteries Do I Need for a 3,000W Inverter?
- How Many Batteries Do I Need for a 5,000-Watt Inverter?
- What Size Battery Backup Do I Need for My Home?
- How Many Batteries Do I Need for Solar? (Sizing Formula + Examples)
Sources and further reading
- Battery University: BU-402 What Is C-rate? explains charge and discharge rates. Also, it discusses capacity and runtime.
- Battery University: BU-409b Charging Lithium Iron Phosphate covers LiFePO4 charging voltages. In addition, it details their behavior.
- U.S. Department of Energy: Inverters and Grid Services Basics: Learn what inverters do. Also, discover their main types.