It took a bit longer for the Nikon to drain, so I when I went to bed, it was still going. At the point where the generics had been depleted, the Nikon was still only just below its nominal voltage.
The discharge curve also looks quite different, much flatter and with a much sharper drop at the end. Total capacity ended up being almost 1170 mAh (@ 250 mA discharge current). More than stated on the battery, but I don't know at which discharge current that was determined.
Lately the replacements felt like they drained rather quickly compared to the Nikon. Not only the lower capacity is to blame, also the much less flat discharge curve probably makes the camera switch off long before that capacity has been used up.
One thing that is often a characteristic of low quality Chinese batteries is high internal resistance, so even if they have decent capacity it's at a voltage that may cause the camera to shut down during current bursts. Your 250mA are conservative, you should probably discharge at 500mA-1A to see how they behave in that case.
YMMV (a lot) with replacement batteries. Over the years I've had some that were pretty OK but visibly less good, some so hopeless that after buying 3 different "replacement" brands I had no choice but to throw them out and buy originals. I've also had some that impressively still worked acceptably after >5 years, when the originals were long dead...
My current camera uses Sony NP-FW50s, I've got 2 originals and 2 very cheap replacements and they just work, I simply can't tell them apart without looking at them.
Thanks for your insights.
I'm still deciding on buying a new original (€ 40) or again a replacement (€ 10-20), but one thing is clear: the bulged generic replacements are going to go.
I think even at 250 mA, which I had arbitrarily chosen, the no name replacements are clearly no match for the original. I will repeat the discharge cycle at 500 mA for all three batteries, but I think the steeper discharge curves of the generics already indicate a higher internal resistance.