Hello, I have a Macbook Pro 15 inch Early 2011 with an aftermarket battery from iFixit (original was replaced due to high cycle count and diminished capacity). I use an application called battery guard that sits in the menubar and gives me information about the battery including health stats. I got this new battery for Christmas a few months ago and it was performing great up until Saturday and showed health ~100% the entire time. Beginning on Saturday, the health has been dropping like a rock. Battery health is currently sitting at 51% on a 257 cycle battery, from 100% on Saturday morning. To give some extra context, my original battery went up to close to 2000 cycles I believe and hovered around 60% health at the end. I'm hoping the battery will stabilize at some still-useful capacity if it doesn't go back up on its own. I'm generally careful about not leaving the laptop plugged in all of the time and baby my computer a lot. I tried running the calibration sequence (search "mac battery calibration") but that made no difference at all. I also opened up the bottom panel of the computer, the battery looked fine and had no visible abnormalities. Worst case scenario involves remembering who bought the battery for me and taking advantage of iFixit's 1 year warranty. I hope to avoid this, so if anybody has any ideas as to what could be causing this and what I could do about it, that would be amazing! Thanks for reading!