Chosen Solution
I purchased a replacement battery in December 2019. Battery life seemed to be dropping off a bit in the last few months. In the last few days it has been terrible. I just checked coconutBattery and it says 459 cycles with only 50.5% design capacity and status is “check battery”. Do iFixit do any long-term testing on their replacement batteries? In my experience new Apple batteries start to experience some degradation after ~2 years but performance remains reasonable for 2-3 years after that depending on usage. This has just dropped off a cliff. I think the original battery it replaced was still at ~70% after 4-5 years. coconutBattery seems to be telling me the replacement has gone from ~90% to 50% in 2 months. It seems slightly suspect that they are warrantied for one year given this behaviour. Is this normal or unlucky?
No, this is not normal. However, not all batteries are perfect. Likely, this is a one-off issue.
A lot of the knockoffs aren’t the same quality as the OEM pack, so these kinds of issues happen more often then with third shift, or genuine batteries. What I would do is recalibrate the pack and see, but more than likely, the battery is flat out worn. For Macs, you want to follow this procedure.
