MB does not see Battery

It's quite possible the battery has died or reached a state where it can't be charged. A battery tester (take it to your local Radio Shack store and let them test it) should say whether it's good or not. After 16 months of no use, it may have gone south. Anyway, it's probably a good idea to let Apple look at it. They can also check the charging circuitry at the same time.

Regards.

Its possible that since the computer was always used on AC power that the charge regulator has fused/shorted/melted and so the battery charge circuit is, for want of a better word, dead.

This is especially common if you are using an 85watt MacBook Pro power block with the MacBook 65watt charge regulator system, however I doubt you're doing this since you say you bought the MacBook specifically.

Its also possible that the battery has 'gone dry' from lack of any activity whatsoever. Apple recommends cycling the battery at least once a month to enable it to keep charge. If this hasn't been done and as you say the MacBook has been kept on mains power, it is likely that this is what happened. There shouldn't be any damage to the computer, and all you need to do is buy a new battery from the Apple Store.

However, I would check the battery whilst you are still in the store just to make sure.

Good luck!

Dæmon