Many models of Dell laptops eventually develop difficulty holding a charge. This is due to the straight connector used in Dell laptop power supplies, as the wires within the connector eventually become bent and useless from the influence of gravity on the cord. Changing the power supply of your laptop will enable you to see whether the issue is with the faulty power supply design or the actual battery.
Unplug the old laptop power supply from the laptop and the wall.
Plug the new power supply into the wall.
Connect the new power supply to the laptop.
If the problem persists, then the problem is with the battery itself. There are no working or moving parts to tinker with inside the battery (nor would you want to without a large amount of technical expertise), so the only solution is to purchase a replacement battery from Dell.