Moving disks to "new" unit after a failure

I've done a little research, but just want to confirm that my plan will work:

Briefly, I have an old ReadyNAS that has failed, so I've purchased a similar unit on ebay. I don't have it yet, but the box says "NV+" and it is the sort that does NOT have a display panel on the bottom. That's like my failed unit. The seller says that it's never been used, and has never turned it on. I'm not sure if he bought it new, since he says he bought it "a few years ago". It's at least five or six years old, right?

It's coming with four drives installed, so I can easily turn it on and see what happens. If it doesn't work, I can replace the coin battery. If it checks out, I should be able to swap in my three disks (same order), and it should work? I actually got a new server recently but had not yet moved everything over, so I'll do that immediately. Then I'll get the latest firmware/software installed on it - I'm a little uncertain on how to do that. The old unit had not been updated for many years - I imagine firmware and software is out of sync, but I've read that this will not prevent the unit from starting up.

So, I'd appreciate hearing that this is a good plan, or of any pitfalls. I'm just a photographer, not a computer geek.

(I keep all important files on a variety of disks, DVDs, locations - there are only "nice to keep" files on the failed unit I want to recover.)

FYI: the old unit failed as follows: I shut it down before leaving town for a week (it is rarely shut down otherwise). When I returned, I walked into the closet and touched it - I guess I do this instinctively - and indeed there was a static discharge. Our absence must have made things drier than usual. I touched it again, and there was a second discharge visible within the front USB port - uh oh. Then I pressed the "on" button and nothing. I replaced the coin battery, and still nothing.