Hi @montymoss welcome to this free user to user Alienware laptop discussion forum. This is not Dell Support.

Please create windows Battery Report to determine if Battery ability to hold charge is now too low. Windows 10 Battery Report: What It Is And How to Use It (lifewire.com) 

For the typical user, noticeable reduction in run time generally will be observed after 18 to 24 months. For a power user, reduction in run time generally may be experienced within 18 months. Dell recommends buying a OEM Dell laptop battery when the run time does not meet your needs. Dell Laptop Battery - Frequently Asked Questions | Dell US 

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ive done a battery report already

Design Capacity 67,990mWh

Full Charge Capacity 3,876mWh

Hi @montymoss thank you for sharing update. Battery Report confirms a new replacement battery is required for continued laptop function. 

A laptop without battery is designed to function as desktop on ac adapter power. 

New Alienware 17 R4 / Alienware 15 R3 Original 6-cell Laptop Battery 99Wh - DP/N 9NJM1 

New Alienware 17 R4 / Alienware 15 R3 Original 4-cell Laptop Battery 68Wh - DP/N 44T2R 

montymoss,

I have had my Alienware 15 R3 for about 2.5 years now

Just an FYI. This 15 R3 originally shipped from Dell 5 years/3 months ago on November 18, 2016. The warranty on the system and battery expired on February 17, 2018.

@montymoss !

You definitely need a replacement battery so heres one on amazon.

Amazon.com: Type 9NJM1 44T2R MG2YH Laptop Battery Replacement for Dell Alienware 17 R4 R5 15 R3 R4 P31E P69F P31E001 P31E002 P69F001 P69F002 HF25D 01D82 546FF 0546FF HF250 0HF250 0MG2YH 99Wh 11.4V 6 Cell : Electronics