JamesBea, you are basically looking for the output numbers. Take a look here at your charger:

https://hobbyking.com/en_us/imax-b6a...___store=en_us

Max Charge: 50W
Max Discharge 5W
Charge Current Range: 0.1 ~ 6.0A
Discharge Current Range: 0.1 ~ 1.0A

Compare that with something more expensive (I'm not recommending this one):
https://hobbyking.com/en_us/0620ac-u...___store=en_us

Maximum Charge Capacity: 300W
Maximum Discharge Capacity: 20W
Maximum Power Capacity: 300W
Charge Current: 0.05 ~ 20A
Discharge Current: 0.05 ~ 20A

That's how you can tell what you are getting for your money with the charger differences. Now, how do those differences help? Mostly by calculating what your charging needs are by using a charging requirements calculator:

Charger and PSU calculator

Amps are what you want to focus on for a single battery charge. The normal charge rate is mAh/100. If you have a 4600mAh battery, the desired amps for charging is 4.6 amps. If you have a charger that cannot do 4.6amps, then your charging will take longer (and will not be as effective). You can crank up the amps over the recommended for faster charging but at risk to damaging the battery over time. The more amps you use, the more power (watts) the battery needs to support it. Wattage also is what helps when charging more than one battery at a time (since you need double the charging capacity).

There is a lot more to it, but hopefully that helps get you started.