2.Some electronic locks are EMP resistant some are not. The recommend the S & G brand of electronic locks for EMP resistant single lock installations
3.Redundant locks give you the best of both worlds , they consist of a mechanical and electronic lock in one , so if one fails the other will allow you access to the safe.
4.Most mechanical lock manufacturers recommend that you have your lock serviced at least every 5 years by a qualified safe technician.
5.Electronic locks are sealed from the factory and if opened will void the warranty from the manufacturer. about the only maintenance is replacing the battery.