Chosen Solution
I had a crappy battery that would last less than an hour on my 2012 Macbook Pro. I ordered a replacement kit from iFixit and followed their guide for swapping batteries. My new battery is fine for a while, but will eventually not be detected within a couple hours or days. I have removed the battery and reinstalled the same one twice, and each time, it’s fine for a bit, but within hours or days, it’s undetected again. What’s going on, and how do iFixit (ha)? coconutBattery screenshots: With undetected battery, plugged into charger:
With battery detected, not plugged into charger:
With battery detected, plugged into charger:
SMC (this is the closest distance I could get my phone to focus at):
Well, it sounds like you have another problem here ;-{ First lets get some better diagnostics, download and install this gem of an App CoconutBattery We need to snapshots one with the MagSafe connected and a second with it removed that way we can see what the system does. Granted this will take a bit of effort (and luck) to get the info. once you do post it here for us to see Adding images to an existing question Update (12/06/2018) The battery sensors within the battery are working! Did you by chance have a liquid spill at some point in the past? Or, get the back edge of your system wet? This looks like the SMC chip logic has corrosion damage. Here is the location of the SMC chip marked in green:
