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Why your outdoorsy friend suddenly has a gummy bear power bank

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258 points arnon | 4 comments | 21 Sep 25 12:31 UTC | HN request time: 0s | source

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cenamus ◴[21 Sep 25 13:07 UTC] No.45322381[source]▶
20Ah for 23 bucks? Seems like it's almost too good to be true. Wouldn't surprise me if it was just half that, would explain the price and weight.
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thegrim33 ◴[21 Sep 25 14:56 UTC] No.45323306[source]▶
Man it drives me crazy when people/products use Ah instead of Wh as a way to specify battery "capability".

Without knowing more details about the battery, "20Ah" alone does not convey enough information to determine how long the battery could power a given load for. If I need to power a 100 watt lightbulb, will a 20Ah battery power it for an hour? 10 hours? 10 days? No way to know.

Wh is the unit of stored energy, Wh is what I want to see. Even the official Amazon product page for it doesn't list a Wh figure.

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esperent ◴[21 Sep 25 16:13 UTC] No.45323988[source]▶
Isn't that 20Ah figure always relative to the internal voltage of the lithium batteries, 3.7v? At least that's what I always assumed.
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nerdsniper ◴[21 Sep 25 20:17 UTC] No.45326275[source]▶
10 years ago most of these battery packs were relative to the 5V output voltage, so they advertised lower amp-hours. That stopped making sense with fast charging at higher voltages so they restandardized on 3.7V.

But watt-hours would make infinitely more sense for all batteries.

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1. xp84 ◴[21 Sep 25 21:50 UTC] No.45326990{3}[source]▶
Then the fact we’ve “standardized” on mah as the unit is just another in our long proud tradition, same reason we still use “Watts” as the main measure of light output, even when it has to be made up for use on LED bulbs.
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2. eru ◴[22 Sep 25 01:10 UTC] No.45328163[source]▶
Could as least use Coulomb (or just count electrons), instead of taking Current = Charge / Time and multiplying by charge again.

For what it's worth: 1 mAh ~ 2.25 * 10^19 electrons. Or with SI-prefixes: 22.5 exa-electrons (= 2.25 Ee).

3. sva_ ◴[22 Sep 25 14:35 UTC] No.45334055[source]▶
Mostly all flashlights advertise in lumen though? I suppose you mean light bulbs?
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4. xp84 ◴[22 Sep 25 17:14 UTC] No.45336492[source]▶
Yes, I mean the bulbs. Generally in the US at least we find them in the store labeled like "40 watt equivalent (small print: 2.1W)"