What are you using to test the batteries?
Hah! I'd written, then deleted, a long rambling few paragraphs about my battery tester from my original post!
I'm using the Philips SBC169 tester (and charger!) of which everyone is obviously familiar
I've had it for a very long time, and unlike some testers it seems pretty good at deciding between marginal and good batteries - the display seems pretty linear in response to battery condition, - with some testers I've tried, the needle either flies to the end or does very little and not much in between.
Looking inside it some years ago, there are some surprisingly chunky resistors, so I imagine it puts a small load on the battery as well as simply measuring the voltage, which seems to me to be A Good Thing.
It also tests a few battery types that are no longer available
It's got a 9 volt input jack, though quite why you'd use this to charge 1 size of battery at a time is a bit beyond me.
Saw one a while back on ebay for around £50!
Ian