I have used plenty of aftermarket batteries. Do yourself a favour and don't bother with them especially the ones on eBay.

They lie about their actual capacity.

They are unreliable over time. They tend to lose capacity a lot quicker.

They tend to cut corners and are not safe... I've experienced one which exploded and another which bulged.

The big corps tries to source the best battery cells. They want to make their devices as small as possible and do not cut corners with safety. Some aftermarket entity doesn't have the same resources nor are they going to be better...

The only aftermarket batteries that has lasted longer are those with bigger dimensions and comes with its own custom battery/back cover. Mugem seems to make quality batteries. Just search for feedbacks/reviews