I routinely charge at 2.5C (20% SOC) and 1C (60% SOC) for most 2Ahr cells. They hardly get warm at all, as long as the total charge time is short (15 minutes). With USB (5V) supply, you can hardly drive it over 1.5C (3A for 2Ahr cell). If the cell does not get warm, then most of the energy is stored instead of heating up due to "Internal Chemical Resistance to Charging". Heat is the biggest problem.