Moving your WhatsApp chats, groups, images and videos from one android based phone to another android based phone is a common "problem" - so here's how I made it work in roughly 6 simple steps:
1. On the new phone:
- install WhatsApp
- verify your phone number and such
(we do this so WhatsApp will init the folder structure)
2. Connect the old phone to your PC, or use a file manager to browse the old phone's folder structure and copy the WhatApp folder, with "Databases", "Media" and etc. - and copy the WhatsApp folder to your PC or to a location on the SDCARD.
3. Now connect your new phone to your PC, or switch SDCARDs between phones.
4. Copy the contents of Databases and Media from the old phone into/over the fresh WhatsApp folder structure on the new phone.
5. On the new phone, delete the WhatsApp app/application.
(Android will remove the WhatsApp app but not the data folder/folder-structure, so this is safe.)
6. Then re-install WhatsApp on the new phone.
Upon WhatsApp startup, verify your number again and then a new step will pop up, asking you to restore an old backup. Select "restore".
(at this point WhatsApp will have detected the .db.crypt8 database files from the old phone, and messages in there will properly link to media found in the Media subfolders, so chats, images and videos will resurface in the app.)
I might be overseeing something obvious, BUT: I really don't understand why WhatsApp, with over a billion users!, doesn't offer a clearer migration path to its users.