Given that the system is likely at least two years old, you are almost certainly seeing battery deterioration from age and use. Run a powercfg /batteryreport from a command prompt with administrator privileges.  It will show you the design and current battery charge capacity.  If you're seeing an appreciable loss of battery capacity, it's time to replace the battery.  2-3 years is about what you can expect before needing a battery. As for the rest, a system with an i9 CPU and that GPU is just not a good candidate for long battery runs -- between the power-hungry CPU, GPU and screen, you likely will never see more than 2 hours, even from a new battery and with drastic power economy settings -- that is, preferably with the nVidia GPU disabled.  The GPU is the biggest consumer of power in that system.  
Hello, I have an out of warranty Alienware m17 R1 running an i9-8950 Intel processor, 32GB RAM, an Nvidia GeForce RTX 2080. We live in an area where power fails frequently. The battery life on the computer is extermely poor. I shut down everything and have the screen as dim as possible and in Task Manager I shut down anything unneeded. The battery still dives from 100% down to 50% in about 20 minutes. It has been known to drop from 40% to 6% suddenly within a few seconds. Even if I have the lid closed on standby it drains the battery. The computer is only 2 years old. My last Alienware 17 R? never had this issue. My wife's Alienware m15 is also having the same issue. I have seen a few things regarding this but everything I have tried is useless. SupportAssist and going into diagnostic mode does not reveal that the battery is the issue. We have an m15 that is having the same issues. I am up to date on all drivers and BIOS as well as the most recent AWCC. I have the settings in there as Thermal: Quiet Mode, Overclocking: Off and Power: Balanced.
m17 R1, battery drain ridiculous