Laptop's battery LED keeps blinking and doesn't charge

1. Acer aspire e15-551g:
2. Battery Health: 71.5% ( from battery report )

Problems:
a) When plugged with adapter, the following happens in the order:

1. Battery is charging (in this state for 2-3 seconds).
2. Battery is not charging (in this state for 1-2 seconds).
3. Battery is charging (in this state for 10-15 seconds).
4. Battery is not charging, both LEDs start blinking, battery icon the screen also blinks with a cross symbol over it. ( in this state forever)

The above behavior happens every single time. I need to do this for 4-5 sometimes 10 times and then the battery will charge without any issue, until next time.

b) When plugged with adapter, but battery is removed ( running on AC ) one of the following things happens

1. The LED lights up for 2-3 seconds, laptop doesn’t turn on and finally the LED turns off
2. The LED lights up for 2-3 seconds, laptop turns on and then shuts downs in another 2-3 seconds.

Sometimes doing the above for 4-5 times makes the laptop work, other times if I boot it after 30 min or an hour there is no issue in booting.

What should I do to resolve this?