Firstly you need to understand how LiPo power packs work. The rating of a Lipo pack is defined by: The number of cells ie voltage, the mAh (milli amps per hour) the available current and the C rating current output.
lets start with the voltage:
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Every motor and ESC combination has a Cell rating, that specifies the maximum operating voltage. Example: a specific motor may specify it can operate with either a 2s or 3s lipo so its operating voltage is 8.4 to 12.6 volts maximum.
The next thing to consider is the mAh rating, the higher the current rating the longer you get to fly before it runs out. The down side's are: the more current capacity you choose the bigger and heavier the battery becomes, so it becomes a trade off between weight and flight time. The other consideration is the ESC (electronic speed controller) rating if the current draw of the motor exceeds the ESC current rating you burn it out, so you need to get the specification correct to start with. The C rating quite simply is the amount of current a specific LiPo can discharge at any point in time. Its more important when there is a high current draw required for example flying EDF powered models.
Flite Test use a term which can be confusing in general modelling circles "Power Pack". They refer to a collection of parts which they supply for a specific model type. For example: The Simple cub, which if memory serves me, is a power pack 2. This comes with a motor, ESC, servos, prop and leads etc. The rating of that motor, prop and ESC will define the optimum Lipo pack you should use and is usually provided.
My understanding of a power pack is: A self-contained transportable unit which stores and supplies electrical power (battery).
As for Lipo chargers that's a matter of opinion and personal choice, I tend to use Imax B6.
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It can operate off mains power, or 12V lead acid battery for charging in the field it comes with a selection of LiPo battery connectors just in case. It will certainly charge all LiPo's up to 4s.
However, I am sure there are plenty of others on the forum with alternative suggestions.
This is just a quick over view hope it helps.