v1.5.1 store with Database v1.5.3 what can go wrong?

After upgrading to 1.5.3 several months ago I was having an issue with my check out process. So, I tried this to see if it would work. I uploaded my old back up, which shares the same database, changed the current zen cart folder to another name and change the back up one to the site name. When I logged into make a purchase it processed everything without any issues. My only issue is I have a bunch of new products in the database without the pictures, but most importantly it says that Zen Cart 1.5.1 with Database 1.5.3 and I am afraid I will run into problems somewhere along the way. I can replace the images, I can't replace "what works" when it comes to functionality. But I am scared to try to upgrade to 1.5.3 - how bad is having a zen cart mismatched with the database, and any suggestions on how to upgrade without once again losing functionality?

Well, it is a somewhat difficult question to answer (how bad is it to have this mismatch) as it is an unsupported condition.

However, that said, if you follow a process of upgrading where you clone your store (including database) each to their own area, you can merrily test the store while continuing to operate under the current setup and then "move" your new store to be the active store... That's probably briefer a description than gives it justice, but that's a basic plan that could be performed.

One link that is relatively helpful with upgrading is brought to you by Dr. Byte at: http://www.zen-cart.com/entry.php?3-How-do-I-rebuild-my-site-on-the-new-version-instead-of-upgrading

In the case of using v1.5.1 PHP code with a v1.5.3 database, the primary issue you'd run into is that customer/admin passwords won't work properly when trying to log in ... this is only triggered for customers/admins who attempted to log in while the v1.5.3 PHP files were in place. They can of course use the Forgotten Password feature to get logged in again.

And then to re-do the upgrade and give yourself a place to test things without impacting your live store, follow the link suggested earlier ... http://www.zen-cart.com/entry.php?3-How-do-I-rebuild-my-site-on-the-new-version-instead-of-upgrading