Nexus 5 flashing red light and optimizing apps

The phones been fine for ages. Its had the red light issue but ive been able to boot it back up before. Anyways, yesterday I gave my sister my charger (Samsung). I havent got a charger now except for the LG one but it charged rediculously slow before. The phone went down to 0% with the lg charger and it powered off and showed a red light which I assume means dead battery. This morning I got a charging icon with my dads HTC One m9 charger. It powered on but it gets onto optimizing apps and powers off around 18 of 198. I tried booting it up without a charger and it went dead again. Now its been charging for around 20 mins flashing red and then it just died and it after unplugging and plugging it back in its starting to flash red. It was stock too