what will happen if i forget to disconnect the battery, when i install new car computer or ECU?

what will happen if i forget to disconnect the battery, when i install new car computer or ECU, i have nissan maxima 92 SE

a sudden surge of electricity will create the need to replace it again. you should be disconnecting the battery and shorting the two cables out to each other to drain the capacitors for the abs and air bag systems and any others.

Car PC 101