You might want to check this post out:
"https://www.quora.com/How-long-approximately-can-30WHrs-2S1P-2-cell-Li-ion-Polymer-laptop-battery-last#:~:text=It%20depends%20on%20the%20draw,will%20last%20about%203.5%20hours. "
But it depends on your laptop specifications.
Try to use your laptop model...