You math it a little confusing when it come to the cooling required. You scale up the power draw to an hour, but then take your cooling based on that. But each individual battery still only needs to dissipate the heat produced during its charge - so in your example, with 60kWh and 99% efficiency, the energy to dissipate is 0.6kWh per charge, over the duration of 5 minutes. Which sounds much more manageable than the 7.2kWh you end up with (which would be for 12 charges over the course of an hour).