Battery lives seem to be extraordinarily variable. I think there are two major issues that play.
One is the quality of manufacture. Tricky one as there aren't actually a lot of battery manufacturers so a lot of badge engineering occurs. You might be safer with a 'known' make, but then again it's not a certainty.
The other issue is how the battery is treated. Most cells can be damaged by shock, so if posted to you and not very well packed they could be damaged before you get them. Obviously if you drop them, etc, yourself you can damage them.
The other treatment issue is charge and discharge. If mishandled electrically - overcharge, over-discharge, shorts, too high rates of charge/discharge, and/or the battery getting too hot during any of those (eg. when charged in situ) - then the battery, or some cells within, can be damaged.
I have a Braun battery shaver with a NiCd which has been going for donkey's years and is still fine. But it has a dedicated charger, is obviously only discharged at it's designed rate and doesn't sit unused for months at a time. Unfortunately not many of our models have the same predictable and well controlled environment, so a higher early death rate is almost inevitable.