Batteries don't last as long as they used to. Now 18 months to 2 years of battery life is common. FAQ - Laptop battery articles - Dell Community
I charged the battery to 100% yesterday again at 1900 hours and then closed all apps and closed lid and stopped charging. Today morning at 9 am when I open battery critically low and laptop will not start till I started charger. This is happening from last many days. Customer care only troubleshooting and diagnostics and battery health excellent showing so all ok as per them. Why battery draining they say they dont know. I paid by taking loan for this machine and now I am stuck and nobody assisting. I called customer care few dozens of times but neither they connect to senior or most of the times calls get disconnected and nobody is bothered. Nobody replies on service requests.   My 10 year old Dell has better battery backup, trust me.
Inspiron 5502, battery complaint