pcmhacking.net

I should probably replace mine as I got mine in 2013 I think?

I still use my original nvram from probably one of the 1st 4 or 5 boards still trucking along like a champ

Yeah it depends on a lot of things, how long it existed before first use (its only then the battery starts being used), how much extreme heat its been subject too, how long its been using power from the car instead etc. It should still get close to 10 years. But if your not tuning its best to put your tune on an eeprom and leave that in the car since it'll work forever. Vlad in your case it might to hurt to keep a spare on the shelf incase you go to tune one day and find its no longer working, but it might work for years yet too.

A quick update.

I've put the DS1245Y chip into my eprom programmer and I can still read the tune file that is loaded on there & verify against what it should be. Wouldn't a flat battery cause it to go blank?
The build date on mine is 1148, so almost hit 10 years.

Yes it would cause it to go blank, but also other strange things can happen when its borderline. I cant say for sure. But if the contents verify OK against what is supposed to be on there (not just that you can see some data) then its also worth checking other things, possibly including the ecm - its possible that its got an internal problem of its own. You can always re-flash the nvram with a fresh copy of a known good bin (make sure it includes the OS segment - look at the end of the file and make sure you see data there), and try again.