Well, if you value battery performance, even no trade in, you also won't use the old batteries if they are not performing. If they are old, you can do a few things: 1. Throw away. 2. Use in low end devices such as your kids' play torchlight. 3. Trade in.
Charger also depends on your requirements. If you are interested in getting a full solution, you need a C9000, followed by a 801D, then another super powerful 1-30 cell high rate charger discharger for matching. But most people will get away with a C9000. If you are just going to have ONE charger, make it the C9000.
So C9000 is good enough instead 810D?