I have a USB meter and tested the charge input of the NiteCore TIP after it got completely drained, it consistently charges around 670-680mAh each time…
it just drains completely after 1 whole day of no usage. So it’s likely a bad battery?
Did’t mean to mislead you, just rough hypothesis. If you like it, just get another one. For me, they are too cheap to mess with. But then, I have no technical skills to attempt it.