You can test the battery:

Open an Administrator CMD prompt (CMD, run as Administrator).
Paste this command, and then press Enter:
powercfg /batteryreport

That will show a figure for the designed battery capacity (when new) and the current ("full charge") capacity.

Your laptop is five years old. If that is the original battery, it is near end of life and failing. It may also be swelling, which can cause touchpad and keyboard issues. I recommend that you open the laptop to check the battery. If it is swelling even a little, you must remove it and safely dispose of it.

You may buy a genuine Dell battery direct from Dell or from Parts-People. (each of those links goes directly to the battery for your laptop model)

Whenever touching components or working inside a computer, wear a grounded wrist strap, also called anti-static wrist strap, ESD wrist strap, or ground bracelet. It's a cheap and sensible precaution. Rest the laptop on an anti-static mat or at least a reasonable alternative such as corrugated cardboard.

Swollen Battery Information and Guidance | Dell Canada