Easy Solar Calc

How long will a 100Ah battery last with a 1000W inverter?

Short answer

At a full 1,000 W load, a 100Ah LiFePO4 battery lasts about 0.9 hours — 55 min — through a 90% inverter, drawing about 86.8 A the whole time. A 12 V 100Ah AGM battery used to 50% lasts about 19 minutes at this current once the Peukert correction is applied — roughly a third as long.

How to work it out

  1. 100 Ah × 12.8 V × 80% usable = 1,024 Wh
  2. 1,000 W ÷ 90% inverter = 1,111.1 W average
  3. 1,024 Wh ÷ 1,111.1 W = 0.9 hours (55 min)

A 1000 W inverter doesn’t use 1000 W by itself — the load does. This page assumes the inverter is running flat out, which is what happens with a microwave, coffee maker or kettle. Lighter loads last proportionally longer.

Adjust for your project

Total amp-hours of the bank (two 100 Ah in parallel = 200 Ah). Lead-acid: the 20-hour rating.
12 V lead-acid, 12.8 V LiFePO4, 24/25.6 V or 48/51.2 V.
Sets how much of the rated capacity you plan to use: 80% for LiFePO4 (Victron rates cycle life at 80% depth of discharge), 50% for lead-acid (Trojan recommends 20–50% for long life).
Running watts of everything on at once
More options: DoD · Inverter eff. · Duty …
%
Blank uses 80% for LiFePO4 and 50% for lead-acid. Check your battery’s data sheet.
%
Victron puts modern inverters above 90%.
%
For anything on a thermostat. A 12 V compressor fridge runs roughly 25–50% of the time (Victron’s example); a household fridge about a third (Virginia Cooperative Extension).
What the inverter uses just being on, all the time it is on. It matters most for small loads left running 24/7 — a CPAP, Starlink, a fridge.
°F
Batteries hold less when cold: Victron gives about 80% for LiFePO4 at 32 °F (0 °C) and 50% at −4 °F (−20 °C); lead-acid about 86% at 32 °F. LiFePO4 must not be charged below 41 °F (5 °C) unless it is self-heating.
Runtime0.9 hours
In hours and minutes
55 min
Usable energy
1,024 Wh
Average draw from the battery
1,111.1 W
Battery current while running
86.8 A

For this job · affiliate link
12 V 100 Ah LiFePO4 battery55 min is short. A second battery in parallel doubles the runtime and halves the current each one carries.
View on Amazon (opens in a new tab)

Runtime at other loads

Runtime at other loads
LoadRuntimeBattery current while running
2536.9 hours2.2 A
5018.4 hours4.3 A
1009.2 hours8.7 A
2004.6 hours17.4 A
5001.8 hours43.4 A
10000.9 hours86.8 A
20000.5 hours173.6 A

What to know about a 1000 W load on 100 Ah

  • Short bursts are fine. A microwave running 5 minutes uses about 93 Wh from the battery — under a tenth of its usable energy. It is long, steady 1000 W loads that a single 100 Ah battery can’t sustain.
  • Current is near the battery’s limit. About 87 A at 12.8 V is close to the 100 A Victron recommends as the continuous limit for its 12.8 V 100 Ah battery. A surge from a motor or compressor can go over it.
  • Lead-acid does much worse here. At this current a 100 Ah lead-acid battery is discharging faster than its 5-hour rate; Trojan’s data shows capacity falling from 105 to 85 Ah between the 20- and 5-hour rates, and it keeps falling.
  • Cables and fuses matter at this current. Wire and fuse sizes come from NEC/ABYC ampacity tables and the equipment manual — have a qualified installer check them.

The current itself is worked out on how many amps a 1000 watt inverter draws. For a gentler load on the same battery, compare how long a 100Ah battery lasts with a 200W load.

Different size? Use the full Battery Runtime Calculator.

What you’ll need

  • 12 V 100 Ah LiFePO4 batteryPremium price

    About 1.28 kWh rated in a box roughly the size of a group 24–31 lead-acid battery at around half the weight. Check the BMS discharge limit and whether it can charge below freezing.

    See options on Amazon (opens in a new tab)
  • Pure sine wave inverter, 1000 WMid-range price

    Enough for a CPAP, laptop, TV and small appliances. Pure sine is the safe choice for anything with a motor or sensitive electronics.

    See options on Amazon (opens in a new tab)
  • Battery monitor with shuntMid-range price

    Counts amp-hours in and out, so you see true state of charge instead of guessing from voltage — which barely moves on a LiFePO4 battery until it is nearly empty.

    See options on Amazon (opens in a new tab)

As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.

Frequently asked questions

How long will a 100Ah battery run a 500 W load on an inverter?

About 1.8 hours (1 h 51 min) on a 12.8 V 100Ah LiFePO4 battery.

How long will two 100Ah batteries last with a 1000W inverter?

About 1.8 hours (1 h 51 min) at full load, with each battery carrying half the current.

How long will a 100Ah AGM battery last with a 1000W inverter?

About 19 min to 50% depth of discharge after the Peukert correction, against 0.5 hours on paper — lead-acid gives up capacity at high current.

Other common sizes

Sources