Guide
What size battery for a 1000W, 2000W or 3000W inverter?
The DC current an inverter draws at 12V, 24V and 48V, and the battery capacity needed for a given runtime.
Short answer: an inverter question has two parts. The battery must hold enough energy for the hours you will run the load, and it must be able to deliver the current the inverter draws—continuously and during surges. A 2000 W load on a 12 V system draws roughly 200 A from the battery; on 48 V it is roughly 50 A.
The numbers below assume 90% inverter efficiency, 85% during surge and 10 W of inverter overhead, with current calculated at a minimum inverter-terminal voltage of 11.2 V, 22.4 V or 44.8 V. Use your own inverter’s datasheet in the calculator.
How much current does an inverter draw from the battery?
DC current ≈ AC watts ÷ (efficiency × battery voltage under load), plus the inverter’s own overhead. Surge assumes 1.5 × the running power.
| Continuous AC load | 12V class | 24V class | 48V class |
|---|---|---|---|
| 1000 W (surge 1500 W) | 100.1 A (surge 158.5 A) | 50.0 A (79.2 A) | 25.0 A (39.6 A) |
| 2000 W (surge 3000 W) | 199.3 A (316.0 A) | 99.7 A (158.0 A) | 49.8 A (79.0 A) |
| 3000 W (surge 4500 W) | 298.5 A (473.6 A) | 149.3 A (236.8 A) | 74.6 A (118.4 A) |
Compare these figures with the battery’s continuous and surge discharge ratings (and the surge duration) on its datasheet. Two identical batteries in parallel share the current only when wired as the manufacturer specifies. Above roughly 150–200 A at 12 V, many builders move to 24 V or 48 V because the current—and everything it demands of cables, fuses and connections—halves with each step.
How much battery for a given runtime?
Capacity for running a load for a set number of hours, with 80% usable depth of discharge and 90% available capacity:
| Load × runtime | Nameplate energy | 12.8 V | 25.6 V | 51.2 V |
|---|---|---|---|---|
| 1000 W × 2 h | 3.09 kWh | 242 Ah | 121 Ah | 61 Ah |
| 2000 W × 1 h | 3.09 kWh | 242 Ah | 121 Ah | 61 Ah |
| 3000 W × 1 h | 4.63 kWh | 362 Ah | 181 Ah | 91 Ah |
| 1000 W × 5 h | 7.72 kWh | 603 Ah | 302 Ah | 151 Ah |
| 2000 W × 3 h | 9.26 kWh | 724 Ah | 362 Ah | 181 Ah |
| 3000 W × 2 h | 9.26 kWh | 724 Ah | 362 Ah | 181 Ah |
The energy is the same at every voltage; only the amp-hour figure changes. Few loads run at full power for hours—use metered daily energy where you can, and the battery bank sizing guide for whole-day planning.
Inverter rating is not the load
A 3000 W inverter running a 600 W load draws current for 600 W, not 3000 W. Size the battery for what you will actually run at the same time, and check that the inverter’s continuous and surge ratings (in W and VA, with their durations) cover motor-starting loads such as fridges, pumps and compressors.
Before you buy
- Inverter DC input range must suit your battery’s full voltage range, including the low-voltage cut-off.
- Battery discharge ratings must cover the inverter’s continuous and surge current.
- Cables, fuse and disconnect are chosen for the current by a qualified installer—not from a voltage-drop figure alone (Safety checklist).
Hardware to compare
Sponsored links. As an Amazon Associate BatteryCaliber earns from qualifying purchases. These open Amazon search results for each category—they are not tested, certified or endorsed products. Check every item’s manufacturer datasheet against your installer’s specification. Affiliate disclosure
12V-class LiFePO4 batteries
Check continuous and surge discharge ratings, low-temperature charge protection and permitted series/parallel use—not just Ah.
Browse on Amazon48V-class server-rack batteries
Confirm actual nominal voltage (often 51.2 V), BMS communication with your inverter and the manufacturer’s paralleling rules.
Browse on AmazonInverter-chargers by DC input voltage
Search by your battery’s voltage class. A voltage keyword in a listing is not proof of compatibility: match the DC input range, continuous and surge ratings (W and VA, with duration) and the battery charge profile.
Class T fuses & holders
Rated current, DC voltage rating and interrupt rating are separate. Your installer must select the device and holder.
Browse on Amazon