What's the difference between pure sine wave and modified sine wave inverters?

Pure sine wave (90-96% efficient) is safe for all electronics and appliances. Modified sine wave (85-90% efficient) is cheaper but can damage sensitive equipment and causes buzzing in motors. Always use pure sine wave for computers, TVs, and medical devices.

Battery Runtime Calculator

How long will your battery last? Enter capacity, voltage, and load — get runtime in hours and minutes, plus a table for common appliances.

Your battery & load

Battery capacity?

Battery voltage?

Load (total watts)?

Inverter efficiency?

Depth of discharge?

Battery runtime at 150W load

11 hr 31 min

Battery capacity2,400 Wh

Usable energy (80% DoD)1,920 Wh

Effective draw from battery167 W

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How to Use This Calculator

Enter battery capacity (Ah) and voltage

The battery capacity in amp-hours (Ah) is printed on the battery label. Common sizes: 50Ah, 100Ah, 200Ah. The battery voltage is the nominal voltage — 12V for a single 12V battery, 24V or 48V if you have batteries wired in series. Ah × Voltage = Wh (watt-hours), the total energy stored.

Enter your load in watts

Add up the wattage of everything you'll run simultaneously. Check the label on each device — it shows watts or amps (multiply amps × voltage to get watts). Use the "Runtime for common loads" table in the results to see how long your battery lasts for individual appliances.

Inverter efficiency

If you're running AC appliances from a DC battery, you need an inverter. The inverter efficiency accounts for energy lost in the DC-to-AC conversion. Pure sine wave inverters (recommended for electronics): 90–96%. Modified sine wave: 85–90%. If you're connecting DC loads directly to the battery (e.g., a 12V fridge, LED strip lights), set efficiency to 100%.

Depth of discharge

The depth of discharge limits how much of the battery you actually use. This protects battery longevity. LiFePO4: 80–95%. Lead-acid: 50%. The calculator applies this automatically to show your true usable energy.

Peukert's effect for lead-acid batteries

Note: this calculator uses a simplified model. Lead-acid batteries exhibit Peukert's effect — they deliver fewer amp-hours at high discharge rates. A 100Ah battery discharged in 1 hour delivers only ~60–70Ah. At 20-hour discharge rate (the rated C20), it delivers the full 100Ah. LiFePO4 batteries are largely immune to Peukert's effect. For very high discharge rates on lead-acid, actual runtime will be shorter than this calculator shows.

The Formula

Battery Wh = Ah × Voltage Usable Wh = Battery Wh × DoD (%) Effective load (from battery) = Appliance watts ÷ Inverter efficiency Runtime (hours) = Usable Wh ÷ Effective load (W) Runtime (min) = fractional hours × 60 Note: Lead-acid batteries discharge less Ah at high rates (Peukert's effect). LiFePO4 batteries are not significantly affected by Peukert's effect.

Example

200Ah 12V lead-acid powering a fridge

A camper has a 200Ah 12V lead-acid battery (AGM) powering a standard 150W fridge through a 90% efficient pure sine wave inverter. They want to keep DoD at 50% to protect the battery.

Battery capacity200Ah at 12V = 2,400 Wh

Depth of discharge50%

Usable energy1,200 Wh

Fridge load150W

Inverter efficiency90%

Effective battery draw167W

Result

Runtime7 hr 11 min

Just over 7 hours of fridge runtime from a 200Ah 12V battery at 50% DoD. If they switched to LiFePO4 (80% DoD), they'd get 11.5 hours from the same capacity. At 100% DoD (LiFePO4 rated max), 14.4 hours. This illustrates why DoD selection matters as much as battery size.

FAQ

What is Peukert's effect and does it affect my runtime? ▼

Peukert's effect is a property of lead-acid batteries: the faster you discharge, the fewer amp-hours you get out. A 100Ah battery discharged in 1 hour (100A draw) might only deliver 70Ah. At the 20-hour rate (5A draw), it delivers the full 100Ah. The Peukert exponent (typically 1.1–1.3 for lead-acid) quantifies this. LiFePO4 batteries have a Peukert exponent very close to 1.0, meaning they're not significantly affected — you get the rated Ah even at high discharge rates. For high-load applications on lead-acid, subtract 15–25% from this calculator's result.

How long will a 100Ah 12V battery last? ▼

A 100Ah 12V battery holds 1,200 Wh (1.2 kWh). At 80% DoD (LiFePO4), you have 960 Wh usable. At various loads: 100W load = 9.6 hours; 200W = 4.8 hours; 500W = 1.9 hours; 1,000W = 58 minutes. These numbers assume a 90% efficient inverter. For direct 12V DC loads with no inverter, runtime is slightly longer.

Can I run a refrigerator on a 12V 100Ah battery? ▼

Yes, but not for long. A standard household fridge draws 100–200W on average. On a 100Ah 12V LiFePO4 (960 Wh usable), that's 5–10 hours. A 100Ah battery won't get you through 24 hours without recharging. For longer fridge runtime, use a 12V compressor fridge (like Iceco or BougeRV) which draws 35–50W — far more efficient — and gets 20+ hours from the same battery.

What's the difference between a pure sine wave and modified sine wave inverter? ▼

A pure sine wave inverter produces AC power identical to grid power — essential for sensitive electronics (computers, TVs, medical equipment, variable-speed motors). Efficiency: 90–96%. A modified sine wave inverter produces a stepped approximation of AC — cheaper but can damage sensitive equipment, causes buzzing in some motors, and runs 5–10% less efficiently. For any modern home appliance or electronic, use pure sine wave. Modified sine is only suitable for simple resistive loads like incandescent bulbs and basic power tools.

How do I add up wattage for multiple appliances? ▼

Simply add the watts of everything running simultaneously. Find wattage on the device label (usually on the back or bottom), in the manual, or by searching "[device name] power consumption watts." For appliances with motors (fridge, AC, pump), use the running wattage, not the startup surge. Your inverter must handle the startup surge, but your battery runtime calculation uses the average running watts. Use a smart plug with energy monitoring to measure actual consumption of unknown devices.