Alienware 13 R3 - laptop shuts down without warning under heavy load ONLY when on battery

I've been an AW13R3 owner for almost 2 years, i bought a used model without warranty in order to have something to bring with me during job travels. For a year or so the laptop has been performing greatly, both with AC and battery mode. However, in the last 3 months or so i've been experiencing some weird issues with it. Basically, when i play with it on battery, when the laptop goes under heavy load (eg recent games like BFV), the laptop first drops FPS dramatically, then shuts off without warning. Do note, that i changed the battery when i bought it because it had a 55% wear, and repasted bo

Question by Das Lawrence on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.