My phone won't turn on

My phone was low battery (20%) before I went into work so I plugged into a fully charged portable battery, turned the phone off, and went into work. After 7 hours I came back to my car and tried to turn on my phone. Instead of turning on it flashed a red light once (same LED as "the phone is dying" light) for about two seconds. I've had it unplugged from the charger, my phone felt cold so I assumed it might be too low of a temperature or something and it's been over an hour of the same response whenever I try to power up.

Did my portable battery fry the phone's battery or something? It hasn't happened before, I've done this many times while leaving the phone on and charging with no problems.