I indeed need to sketch my use situation.
I like walking around with my synths, hence the battery. But I don't like the micro usb cable sticking out. I think the connector is too fragile. Therefore I keep the battery inside my enclosure. For my other 2 axo's I use a USB power bank inside the enclosure (which I can open to remove the bank to charge).
On the other hand I regularly (almost daily connect them to the Patcher. That is why I like the battery to be charged from the micro usb power, so I never run out of battery power. This would really be an ideal situation.
Great that the 5v pin is bidirectional, thanks for confirming.
I used the StepUp module in my previous axo's cause if you feed 12v through the barrel connector the core switches fluently from usb power to barrel DC power and vice versa when the battery is empty/removed.
I would like to be sure though whether it would be a problem to connect the battery to 5v and plug in the micro-usb in the same time since there is no switching mechanism...