battery cannot suddenly when using ext battery

tonyliu222 your question is a bit cryptic. It sounds like your Redmi Note 3 is not charging. Check your charger first. Make sure it provides proper voltage to your Redmi. then check your cable. After that check your charging port for any bend pins, debris or corrosion. Clean it with a few puffs of compressed air. If all of those things check out, replace the battery and see if that works. If it does not you are most likely having issues with the charging circuit on your board. Use this teardown Xiaomi Redmi Note 3 Reparabilitäts-Bewertung to at least get to your phone's inside.