sounds like a dead batery Click the apple, then about this mac. Then click more info, then system report. when that pops up scroll to the power section and click that. look for charge info. what is full charge capacity, cycle count and condition. The main things are cycle count and condition. modern macs should have a life span of 1000 cycles. the condition should be normal. Any thing less it needs to be replaced or on its way out. Thats why you get the red light. google your mac to see what full charge capacity from the factory should be and compair it to yours.
This is mine from late 2010 MBA
Charge Remaining (mAh): 1490
Fully Charged: No
Full Charge Capacity (mAh): 4539
Cycle Count: 87
my battery is 1 year old because I had a defective on from the get go. Got it replace a year into ownership My full charge from factory was 4680 but now is 4539. That number goes up and down depending on usage