Hi @hanzlahassan
Connect the charger to the laptop and fully charge the battery and then turn on the laptop. Leave the charger connected to the laptop so that the laptop stays on.
If Win10 is installed, when the laptop has fully booted, create a [https://www.windowscentral.com/generate-battery-report-windows-10|battery report]
When you have the battery report, compare the ''Design Capacity'' value versus the ''Full Charge Capacity'' value of the battery as seen in the report. For a good battery they should nearly be the same value.
You can work out the condition of the battery as a percentage by using the formula ''Full Charge Capacity value x 100 ÷ Design Capacity value.'' If the battery percentage is <35% consider replacing the battery.
Here's the ifixit [guide|126899] guide that shows how to replace the battery.
Search online for [https://www.google.com/search?client=firefox-b-d&q=ac14b8k+battery|AC14B8K battery] to find battery suppliers that suit you best. (supplier examples only)