Flashing battery light. NEW PROBLEMS

[Matt]

Getting a flashing battery light, goes dim then bright
So does the mileage, goes dim then bright at the same time as battery light 

Also erratic idle, fluctuates between 900-1100rpm 

All this happens at the same time. 
It's a weird one, happens all at the same time, nothing's been touched. Drove home and it did this from the next startup

Halp. Plsthxbye