This article discusses whether you can use firmware from an older BackPack version on a newer Backpack

Each version of Elo BackPack has different firmware - these are not interchangeable. 
For example: you cannot flash BackPack 2.0 or 3.0 firmware on a BackPack 4.0 device or vice versa.
The reason for this is because each BackPack version has different internal hardware components which do not share the same firmware.