i accidentally put a battery in backwards. i turned it on and the battery got super hot. i took it out and now it won’t turn on with a usb plugged in.
please tell me it’s not hosed.
Unfortunately, nobody’s going to tell you that.
Just inserting it the wrong way is enough. You don’t need to – and can’t – ‘switch it on’ at all.
i don’t understand the last sentence
Just inserting the batteries the wrong way round ist sufficient to kill the board. No need to push the power button. It has no function at all when the battery polarity ist reversed.
no way to fix i imagine then?
I’m no electronics expert, but it might help to replace the IC responsible for the power supply and the charging process. I expect other members with more practical experience will weigh in on this.
easier to just get a new mainboard from alex@clockworkpi.com, check the pico outside of the picocalc and hope the screen is ok (which it probably will be)
once magic smoke leaves an electronic device there’s no putting it back in, there’s only replacing it
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Not that simple, see AXP2101 PMU eFuse configuration after replacement – help needed
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I see why putting one cell in reverse when they are in parallel is one fun way to make pyrotechnics, as is putting different and unbalanced cells since the chip is single cell and afaik doesn’t have the means to balance them (they do balance on their own, but they will do it with 
passion)
But looking at both the datasheet and the board schematics I don’t see even a single puny schottky :c
I know that for the reasons I described before reverse polarity protection would still be pretty useless, but still it would be a nice to have
Also this is speculation on my side, but I guess the fact that the pmu itself doesn’t provide reverse polarity protection makes me think that it’s more intended for use in devices without (easily) user swappable batteries?
That may well be the case.
I suspect that reverse-polarity protection will involve the use of a diode. And diodes cause a voltage drop. And you’ll want to avoid that in our devices, as 3.7 volts is already fairly low.
But as I said, I’m no expert.
Yeah, the voltage drop is indeed a big problem. A Schottky diode has a far lower forward drop and is way more efficient, and you can use a P-channel MOSFET to have even higher efficiency, but this does increase cost and wouldn’t still be enough with the two cells in parallel the way they are :c
A Schottky diode and a boost converter would have solved both issues of reverse polarity protection and voltage drop. Pololu Adjustable Boost Regulator 4-25V
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It’s not that simple.
The voltage boosters result in a further loss. To ensure the maximum current is sufficient, the booster would also need to be significantly more powerful than the simple circuit linked to.
It is much easier to make sure the batteries are inserted with the correct polarity orientation.
a fuse and diode shunt wouldn`t have hurt though, and only added pennies to the overall cost.
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Simply mark the positive ends of the batteries in red (with a pen or tape) and also apply a red mark to the positive terminals’ side of the battery holder.
That should then be noticeable even if you insert them carelessly.
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I agree, would be nice to see a clockworkpi v3.0 board with this
exactly what i did 