Usage and how to charge your battery is the biggest issue for many no matter who’s battery you buy.
As to IFixit’s batteries they generally hold up well.
COVID has messed up raw materials and manufacturing of the battery makers across the board. Many have shipped out bad batts, I know a few folks who had to shell out for a second battery as the seller offered only 30/60 days. At least iFixit offers a full year!
The best thing is to watch your cycle count and the batteries age both have limits. To extend your batteries life don’t do deep discharge events to often as they are the worse for your battery. Likewise recharge before you drop below the 1/4 point of charge. If you are not planning on using the system for a month or more make sure the battery is half charged and lastly don’t store or run the system in temp extremes! Below 40🥶 or higher than 80🥵 Fahrenheit.
To help you monitor things I strongly recommend using a good battery/power monitoring app like CoconutBattery
If you think you have an issue post a snapshot of the apps main window with the battery tab exposed here for us to see while the charger is charging.