Cloning and battery

Hi!
First message here! I received 2 upboards few days ago and I'm quite amazed for its power and features... great board!
I tried a lot of boards mainly based on ARM in the past, I must admit that some choices made by the upboard manufacturer seems a little bit strange for me.
First of all the choice of having eMMC internally: in this way is not possible to remove it for copy/clone easily, second, no support for another external storage device maybe SDcard or something...
Accordingly, this is my experience and my questions for who would like to help me!
Done all explained here (https://up-community.org/wiki/Installing_ubilinux) for intalling UBILINUX ... it works and I have my board up and running.
I modified ubilinux to fit my need... now it's time to clone the image:
Done all explained here https://up-community.org/forum/general-discussion/794-cloning-a-board#2523 .No success at all! I can see that files are inside the eMMC but it doesn't want to boot! and it remains on EFI shell: what I need to do from here?
Then I went on experimenting with the only one (of two) working with ubilinux... at some point I had the great idea to remove the battery... voilà now I have 2 not working boards with only the EFI shell!
So, at this point, I don't know how to do... any advice?
As I side note, I would like to understand WHY it doesn't boot... what is the connection between the boot files in the eMMC and the EFI? I don't like the battery very much and I don't like the idea of having one board not booting up once the battery is exhaust... any way to have these board working with ubilinux without battery?
Another thing: it is possible to access the internal eMMC externally?
I know that probably most of these questions already had a reply in the forum, I spent hours reading and trying and I'm sure I red all about but still can't understand what I asked in this post.
I really appreciate an help... I don't want to give up!

thanks!

Andrea