charger speed?

What makes a fast charger... fast? I'm looking for the technical details.
I ask in regards to cell phone chargers
It would seem that there aren't really "fast chargers" any longer, but a
couple years ago I had 3 cell phone chargers, two for the wall and one for the car. The wall chargers, one came with the phone and it was fast, and one I bought at Wal-Mart for a trip, and it charged the phone noticeably slower. The car charger that I bought was pretty slow also. I'm wondering what is the difference between the two chargers?
Thank you
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In general, fast charge or rapid charge means about a one hour recharge. The higher the charging current the more the battery heats up under charge. This reduces the number of recharges before capacity is diminished.
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