Normally I use this power bank only for powering Raspberry Pi Zero and Arduino projects but recently a viewer mentioned that he had problems charging his phone with it. I tested this on mine and found a problem with a bad soldering joint that caused the phone (Samsung A40) to complain and charge very slowly. The bad solder joint might be a one-off but by the looks of it could also be a more common problem. Unfortunately the fix is not a clear-cut thing because you may end up with a power bank that is not able to charge your phone at all.<br /><br />My previous review of this power bank: <a href="https://youtu.be/eHKbtBkfxKM" target="_blank" rel="nofollow">https://youtu.be/eHKbtBkfxKM</a><br /><br />The Maxim tutorial I mentioned: <a href="https://www.maximintegrated.com/en/design/technical-documents/tutorials/5/5801.html" target="_blank" rel="nofollow">https://www.maximintegrated.com/en/design/technical-documents/tutorials/5/5801.html</a><br />...<br /><a href="https://www.youtube.com/watch?v=LSrtbNV9vt4" target="_blank" rel="nofollow">https://www.youtube.com/watch?v=LSrtbNV9vt4</a>