2 questions: battery life and trade-in

Hello, 


I'm considering trading in my iPod 5th gen for a 6th gen, since I've had it for nearly two years and have come to realize in the last month or two that it no longer has much battery capacity (it lasts almost an hour and a half playing music from my library and using Safari for 20 mins or so, no other background program open, at 1/3 backlight brightness; if I try to play a game or take pictures, I'm lucky if it lasts 15-20 minutes after a full charge.) Rather than get the battery replaced, I'd rather get the newer model, mainly because it has double the RAM and would be able to handle games that my current device cannot.


I've got 2 questions:

1. With the way I use it, what is the best way to preserve battery life in my next device? I keep it plugged in while listening to it during a full day at work, and then at night I also keep it plugged in while I listen to music/videos to fall asleep, and need it in the morning as it serves as my alarm clock. Is it better for the battery life to let the battery become nearly depleted at work before plugging it in, rather than keeping it plugged in all day?

2. Since my current one is still in good shape aside from the battery, I'd like to trade it in at Best Buy when buying the new one. Besides resetting it to factory settings, is there anything else I need to do to prepare it, or make sure that the new user won't gain access to anything of mine?