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Originally Posted by Renate
Maybe I've stated that poorly. Every device requires large start-up current that is usually in excess of what the USB can deliver (unless it's a Type C wih PD).
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That doesn't sound right. If it were, devices powered via USB only (with no battery at all) would not be a thing - and yet they are ubiquitous, including devices with a high startup current.
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In any case, what I meant is you can't just connect a power supply to red and black of where a battery used to go and get the thing to boot (unless it only uses two wires). The 3rd and 4th (if present) have to be connected to something that say, "I'm a battery!"
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I think we're on the same page now :-). I did initially think you were saying that you could chuck something there that *appeared* to be a battery, but delivered no useful power. The Poke 2 is the only device I have ever encountered that *requires* battery power (i.e. useful current, not just battery presence) to at least partially boot before it can start to utilise power from the USB port.
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Here's a plot I did of something (I forget what) but you can see that it peaked at a good 1.4 Amperes when booting! Most devices hit at least 1 Ampere.
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Most USB chargers supply at least 1A, and modern ones a lot more than that.
If you were trying to run the thing from a 500ma computer port, I could see your point... but that isn't a realistic limitation when we're talking about chargers.