Is this the charger you have http://www.chainreactioncycles.com/M...?ModelID=14852
, if so, that will not fully charge a 4200, probably not even a 3300. The problem is a timed charger such as that one will only charge 30min at a 3 amp max. For a 4200 batt it takes at least 45min at 5amps. Timed chargers are not really used anymore, if I were you I wouldn't worry about upgrading your batteries right now, and save up for a decent Peak charger that will be able to get a full charge into the newer batts. Here are a couple of Decent mildly priced Peak chargers I would go with
1.Duratrax Piranha http://www2.towerhobbies.com/cgi-bin...?&I=LXCLD5&P=7
, AC/DC charger, will charge at 3Amps with AC, 5Amps with a DC Power supply such as http://www2.towerhobbies.com/cgi-bin...?&I=LXUF47&P=7
, This Power supply will work fine with this charger
2.MRC Super Brain 960 http://www2.towerhobbies.com/cgi-bin...?&I=LXRST9&P=7
, This charger will charge up to 4.5Amps with either AC or DC
Or you can go to the For Sale thread and find something there. Keep in mind most of the chargers people are selling here are DC and will require a Power Supply. When perchasing a Power supply make sure it meets the needs of the Charger.