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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: 0.003s | source

https://archive.ph/1G2Ut
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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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1. mattmaroon ◴[21 Sep 25 22:57 UTC] No.45327422[source]▶
I think they really just do it because generally everything you will connect to the battery, for the most part, will be using the same voltage, and it’s just easier to do your math and in your head. Remember, most people can’t just calculate a 20% tip in their head without having to think about it for a while or use an app.

Also, in this particular instance, phone batteries are measured in miliamp hours, so it makes the thing I actually want to know, how many times can it charge my cell phone, really easy to figure out.

But as somebody who tinkers with inverters and such, I agree, it is annoying. It is still generally not that hard to do in my head, and trivial with a calculator. But I’m with you.

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2. eru ◴[22 Sep 25 01:05 UTC] No.45328133[source]▶
Well, and if you are on that train: instead of Wh, why not use J?

(Though for American hikers it would be somewhat fun to use a unit of 'pound feet'.)

3. bmicraft ◴[22 Sep 25 19:39 UTC] No.45338446[source]▶
That's wrong, if they only specifiy Ah, then they usually imply cell voltage (3.7V avg.) and not the 5V you're drawing over USB.

Even if you assume you're charging a phone with that, you first need to subtract 25-40% total losses. And then consider that phone batteries are LiHV with 3.85-3.9V nowadays.

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4. mattmaroon ◴[25 Sep 25 16:14 UTC] No.45374717[source]▶
That’s a fair point. I guess I’m thinking of 12v world, like I experience in my RVs and food trucks, where the battery powers everything and it’s all 12v.