Yes please buy the specific charger for your phone. I too have a blackberry (they are so darn chic and smart) and I was using an old, no-name car charger for it. At first, the charger worked for a little while then it completely stopped charging my phone. When I needed my phone the most I was lost in a city, at night, with a phone going dead and a charger that did not work. A friend gave me his blackberry-custom car charger and it hasn't stopped working since;) It's so worth the extra money

The charger has probably died — shorted out internally. If the cig lighter works OK, it's the charger. Chargers draw far less current than lighters do.

Yes, it should work without any problems

Sounds like the battery will not hold a charge. A new battery is required…. and can cost up to $60.

You can buy a car charger with interchangable plugs. Radio Shack and Frye's have them. There's probably other places you can get one too.
That's what I did. Now every time I get a new phone, I just have to buy an adapter. It works well.

Check under those annoying little rubber flaps, sometimes they seem permanently stuck down but aren't.

Yes it may harm its internal charging system
Simply because the B.Berry does not use same power, Voltage and Current as your Mp3 player
It would not have to harm the main battery unless the B.berry short circuits
Please dont try it out.