Battery charger explanation as easy as possible

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There is a lot more to battery chargers but I hope that this clears up the most common questions I'm asked.
Chargers I used in this video (in no particular order):
Variable voltage ( up to 120v) variable current (up to 15a) charger/power supply
Junsi iCharger 406 Duo
Turnigy Accucell 6 (50w)
Turnigy Accucell 6 (80w)
75.6v 2.5a charger
The server power supply was from eBay - they're readily available but they do need modification to get them working.
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