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Understanding Wh vs mAh
What's the difference?
Milliamp Hours (mAh) measures charge capacity at a specific voltage — how much current a battery can deliver over time. Watt Hours (Wh) measures total energy stored, which is more accurate for comparing batteries at different voltages.
Why voltage matters
The same battery has different mAh ratings depending on the voltage used for conversion. This is why mAh alone can be misleading:
- 3.7V — Internal lithium cell voltage (highest mAh number)
- 5V — Standard USB output (what most power banks advertise)
- 9V / 12V — Quick Charge and car adapter voltages
- 20V — USB Power Delivery for laptops (lowest mAh number)
Airline battery limits
Airlines regulate batteries by Wh, not mAh. Knowing your battery's Wh rating is essential for travel:
Under 100 Wh
Carry-on allowed without approval. Most phone power banks (up to ~27,000 mAh at 3.7V)
100–160 Wh
Carry-on with airline approval. Larger laptop power banks (~27,000–43,000 mAh at 3.7V)
Real-world examples
Tesla Powerwall in mAh
A 13,500 Wh Powerwall at ~50V = 270,000 mAh. That is equivalent to 13.5 typical 20,000 mAh power banks — highlighting the scale difference between portable and home energy storage.
Portable solar generator USB capacity
At 5V USB
500 Wh power station = 100,000 mAh
At 20V USB-C PD
Same 500 Wh = only 25,000 mAh
The same battery has drastically different mAh numbers depending on output voltage. Always compare in Wh for accuracy.
Small solar battery as a power bank
A 12V 7Ah sealed lead-acid battery (84 Wh) converts to 16,800 mAh at 5V USB output. Roughly equal to a 20,000 mAh power bank, but weighs 5 lbs vs 12 oz.
When you'll need this conversion
A 300 Wh portable power station at 5V = 60,000 mAh equivalent — equal to three 20,000 mAh banks. But the power station also provides 12V DC and 120V AC, making it more versatile for solar charging.
A 12V 20Ah solar battery (240 Wh) converts to 48,000 mAh at 5V. Each smartphone needs ~19 Wh per charge, yielding about 10 charges after conversion losses.
Charging 50 phones (950 Wh total) = 190,000 mAh at 5V. Choose between ten 20,000 mAh power banks or a 1,000 Wh power station with a 200W solar panel for continuous replenishment.
