I've only got a little one (Sentry 14) but I waived off the idea of electronic locks after seeing enough bad things written and commented about them.
The last thing I want is a FUBAR'ed electrical device standing between me and and my weapons if I have an IMMEDIATE need to access them.
In my case I put a battery operated power failure light on the wall above and behind (as you're standing at the safe door). It serves two purposes. The first is that it illuminates the safe with plenty of light to dial the combo. The second is that it's near the front door and provides light down the hallway. It's the perfect "follow the light to exit" device.
I also keep a chemlight attached to the door frame of the safe so even if for some reason the power fail light fails
, I have a way of getting in.