The Pono charge circuit does get warm when charging at maximum of 0.5 Amps. The battery, if we have done our job well, will not. The following test was done with a depleted battery.
In photo 1, you can see I have connected the USB charger and the protection board temperature is elevated at 31 degrees C after 1 or 2 minutes of charging. Ambient temperature is 24 degrees C.
In photo 2 the minus terminal of the battery is is 25 degrees C and rising. Eventually the whole battery reached ~30 C.
In photo 3 you see the business of charging heats up U50 quite a lot. The maximum temperature I found was 66 degrees C, the related components were also warm. I think this is normal and working as designed. After an hour of charging the battery voltage climbed, charge current fell and the temperature of U50 dropped to 40 C.
So the Pono after receiving a new battery will get warm (as it did when it was new). The end by the USB on the front panel is the warmest spot.
My rule of thumb is - around 60 C you will pull your finger off a hot IC. So U50 is too hot to touch at 66 C but safe. With the shell closed things could get even a little bit warmer but still that is normal and as designed.
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