TETRIS BENTO TUTORIAL • 6 MIN READ

How to Calculate Solar Generator Battery Run Time (Step-by-Step)

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Written by Mark Jensen, PECertified Off-Grid Electrical Engineer • Certified Field Protocol
Modular 3D Tetris blocks representing solar battery station power calculation
The Modular Energy Principle: Think of watt-hours as discrete Tetris blocks. Each appliance consumes a specific block height from your power station stack until depleted.

If you just bought an EcoFlow, Jackery, or Bluetti power station, you probably noticed the box says "1000 Watt-Hours (Wh)". But when you plug in your 100-watt mini fridge, it dies in 8 hours instead of 10. Why?

You didn't get ripped off — you just got hit by the Inverter Efficiency Tax. In this guide, we'll teach you the exact modular formula used by electrical engineers so you can predict exact battery runtime down to the minute.

⚡ THE GOLDEN FORMULA
Actual Hours = (Rated Battery Wh × 0.85) ÷ Appliance Watts

Always multiply total Wh by 0.85 to account for the pure sine wave inverter DC-to-AC conversion loss and battery management system (BMS) reserve.

01Decode Usable Wh (The 85% Efficiency Rule)

Your power station stores direct current (DC) energy in its internal lithium iron phosphate (LiFePO4) cells. But home appliances (like your TV, blender, or fridge) run on alternating current (AC).

The built-in inverter converts DC to AC, and that process creates heat. High-end inverters operate at 85% to 90% efficiency.

Tetris Math: If your station is 1,024 Wh (like the EcoFlow DELTA 2), your real usable budget is:
1,024 Wh × 0.85 = 870.4 Usable Watt-Hours.
02Separate Running Watts from Surge Spikes

Appliances with compressors or electric motors (refrigerators, blenders, power tools, water pumps) need 3x to 5x their normal wattage for the first 2 seconds to kickstart the motor.

  • Continuous (Running) Watts: What it uses while humming along.
  • Surge (Peak) Watts: The initial burst when the compressor kicks on.
03Identify Your Appliance Consumption

Here is what common off-grid appliances actually pull from an AC inverter:

ApplianceAverage WattsSurge WattsExpected Run on 1000Wh
ResMed CPAP (No Heat)35W - 45W45W~21.7 Hours
12V Car Refrigerator (Dometic)45W - 60W150W~14.5 Hours
Starlink Standard Dishy50W - 75W100W~14.0 Hours
MacBook Pro 16" Fast Charge96W - 140W140W~7.5 Full Charges
⚡ DIRECTORY VERIFIED

Verified Power Stations Tested Against This Formula

Open Full Database (6) ➔

Cross-referenced against our 85% inverter discharge benchmark. Compare real Wh ratings before buying:

EcoFlow⭐ 4.8

EcoFlow DELTA 2

Real Capacity:1024 Wh
Continuous Output:1800 W
Mini-Fridge Run Time:14.5 Hours
$799 USDCompare Specs ➔
Jackery⭐ 4.7

Jackery Explorer 1000 Plus

Real Capacity:1264 Wh
Continuous Output:2000 W
Mini-Fridge Run Time:17.9 Hours
$999 USDCompare Specs ➔
Anker⭐ 4.9

Anker SOLIX C1000

Real Capacity:1056 Wh
Continuous Output:1800 W
Mini-Fridge Run Time:15.0 Hours
$749 USDCompare Specs ➔
04Run the Calculation with a Real Example

Let's calculate how long an EcoFlow DELTA 2 (1,024 Wh) will power a 50W Starlink terminal in your camper van:

Step A: Apply Inverter Efficiency1,024 Wh × 0.85 = 870.4 Usable Wh
Step B: Divide by Device Draw870.4 Wh ÷ 50 Watts = 17.40 Hours
Verdict:Your Starlink will run continuously for 17 hours and 24 minutes on a full charge.
05Watch Out for Inverter "Phantom Drain"

Here is the biggest rookie mistake: leaving the AC button turned ON when nothing is plugged in.

A 1,800W pure sine inverter consumes between 15W and 25W per hour just staying awake waiting for something to be plugged in. Over a 10-hour night, that's 200Wh lost to thin air!

💡 Pro Tip: Whenever possible, power 12V DC devices (like car fridges and USB-C laptops) directly from the 12V cigarette lighter port or USB-C PD port. That bypasses the inverter completely and yields 95% efficiency!
FREE OFF-GRID TOOL

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