I have one of these chargers, and they are very good for the money that you pay for them. Instead of buying a field charger that can do two batteries at once, just buy two of these chargers and then you will have two battery capabilities and still have the versatility of a charger that can cycle, charge, discharge, balance lipo's, etc...

[link=http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=7028]Turnigy Accucel 6 Charger[/link]

As for your question, I think really the only way to know if a battery is good or not is to check the capacity by fully charging and then discharging the battery. If it is less than 80% of the original capacity, then it is probably time to get a new battery.