What's the values for the various Heatsinks in Ingress?

I know that rare Heatsink halves the cooldown time, and two rare heatsinks divide it by 4. But what about common and very rare heatsinks?

Solution 1:

Basing on this analysis, these are the values of the Heatsink Mods reductions:

Common: -20%
Rare: -50%
Very Rare: -70%

Every additional mod applies its reduction on the previous modified value, so 2 Common Heatsinks will reduce the cooldown to 64% of the base value (3.2 minutes), 3 Common Heatsinks to 51.2%(2.56 minutes) and 4 will reduce the cooldown to 40,96% of its base value(~2 minutes). The final values are probably rounded.