Battery on Lenovo laptop don't keep charge?

It is either two things:
A) the battery is bad
B) the charger is bad

It is hard to tell which one or if both of them are bad. Do you have a back up charger you can test? If not I would replace the battery first and then if the issue still happens then get a new charger.

The battery would cost around 30 and the charger would cost around 30 also.

Batteries naturally stop holding a proper charge, usually about after a year of full use. This is normal for anything that uses a battery.