Since no one else has answered, I'll offer what little knowledge I have. The quickest, cheapest and easiest way is to use a simple battery tester, like this one. http://www.dealextreme.com/details.dx/sku.4310 It's not exactly accurate, but it's something and you can quickly find the really dead cells fresh off the charger. To get more definitive results, you should get a charger/analyzer. There are a few charger threads here in the forum that might point you to some options. I believe the current popular charger/analyzers are the Maha C-9000, and La Crosse BC-700 and BC-900. If you have any particular questions about any of them, you might try asking in their respective threads.
Best way would be to get a decent charger (Maha, LaCrosse) and have them measure your cell.
An easy basic test would be to charge them, put them aside for 2 weeks and then test the runtime in your favorite appliance.
Another important test would be measuring the internal resistance, but you need a special meter or at least some deeper electrical knowledge to do that.
What are they doing and what kind of batteries are they? Energizer 2500's by any chance? Those and most other 2500 mah batteries are well known for all the wrong reasons :sick2: