or do your own search on laptop battery care or laptop battery best practice.
We've got laptop batteries in the office which are permanently plugged in. If they are unplugged and used off mains, they last about 5 minutes - in fact, some of them report error messages and won't boot due to lack of power.
Best action for you now is to fully discharge / fully charge cycle for about a week. If there's no improvement, you'll have to assess whether the cost of a new battery is worth it - will you ever actually use it standalone . . . ?: