According to the Garmin experts in the class I took. Switching power and ground is about the only way to damage a unit with 12 Volts. They also warned us about powering up for the first time on a battery that might die during the initial software loading.
Get the manuals and follow them. They have detailed instructions on powering the units up for the first time.
Building my RV-10 since Oct 5th 2014
Flying .. once I figure out how to pay for everything
Dues paid 2018