RE: multi charger for aerobird challenger
Your choices for multi-port, peak detect chargers are pretty slim. Most can only charge one battery at a time. One of the big reasons for this is that manufacturers feel the cost of such an item would scare off most buyers. That inexpensive $40 Hitec CG340 (which I highly recommend) would cost $80 in a 2-port version, because to make a 2-port charger, you basically have to put two one-port chargers in the same box. Imagine a 2-port version of the $129 Great Planes Triton. At $258, the demand for such an item would be small.
You want a charger that can do peak-detect, that is, it can tell when the battery is full automatically. You also want a charger that can charge more than 8 cells, so you don't have to buy another one later when you go to larger airplanes. That's why I like the Hitec CG340. It's inexpensive, easy to use, compact, capable of charging up to 16 cells, and it does the job well.
Like most chargers, the CG340 is a 12V DC-only charger. You need some sort of 12V power supply to run it, like a car battery. There are two main reasons for this. First, the charger would no longer be compact, lightweight and portable if it also contained an AC power supply capable of running it at its full capacity. Who wants to lug a heavy brick to the flying field? Second, adding an AC power supply would drive the price up, again scaring off buyers.