Lost all apps and related data when battery was replaced

I have a generic android tablet which needed its battery replaced. Prior to replacing the battery (I already successfully replaced the battery using soldering tools etc), I had apps with related data, folders on a rooted tablet that used android 4.2.

My assumption here is that all my apps and data were safely stored in internal flash and that replacing the battery would NOT cause me to lose any of my apps and related data.

Unfortunately after I successfully replaced the battery the system came up as if the tablet were being used for the first time (system asked for initial setup info) and all my apps, data and folders previously created were all gone.

This makes absolutely no sense. This is akin to me removing power to my hard disk and restoring power again to the hard disk. No app and data should be lost. Can anybody explained why this happened and is there anything I can do to get my apps and related data back as they had existed prior to replacing the battery?

Thanks