Disabling Mini2 from turning off when disconnected from external power source

Not that I can find.

Can you describe the steps.  I'm not seeing this behavior. If i turn mini 2 on and then connect to power brick to charge and then disconnect, the mini 2 stays on.

this is different than the original. The mini 2 has USB mode.

Under System Settings, if you change the USB mode to Garmin instead of Mass Storage. does that change the behavior you're seeing?

Ahhhh!! Woohoo!! That worked! Jason Pursell you are a gentleman and a scholar :) 

I get different behavior when connecting to computer (where Garmin Express is) or just wall charger/power brick.  If I connect to computer it just automatically puts it into MTP mode. The only difference is that if the device is set to Garmin Mode and I plug it into the computer, the Mini 2 BRIEFLY asks me if I want to put the device into MTP mode. However, it doesn't matter if I say yes or no (or not answer at all).  If connecting to a computer it will just put it into MTP mode automatically.

I would not expect the USB behavior (Garmin vs. USB mode) to affect a non-computer connection. The whole question of "what USB mode" is ONLY relevant to a computer connection. Meaningless on a wall wart, power bank, or whatever.

I do not know about the M2. On a "normal" Garmin handheld, the distinction is:

Mass storage means "make the device visible to Windows Explorer as a removable device", This might be as a removable USB "disk". Or it might be in Media Transfer Protocol mode (MTP). Or you might be asked.

Garmin mode typically means Garmin spanner mode. This allows the device to output GPS information over the USB link for use by an application on the PC. In some cases, this requires the use of a virtual serial port (which converts USB to serial, which is what the PC application might want to see).

This is not to say that USB mode does NOT affect a charge-only connection. Just that doing it that was is pointlessly obscure. Like a lot of the M2 user interface.

Oddly it does. When "Garmin" mode is selected on the Mini 2 and it is drawing power from a power bank the unit remains on when unplugged from the external power source. When the Mini 2 is in "USB" mode and the same situation is applied it automatically shuts off. I agree on the obscurity of the interface and I'm not sure if this was the intended outcome from Garmin, but it works so I'm happy. I put in a ticket with Garmin about this. Maybe they'll add the menue option back for the unit to stay on like it is with the original Mini since that was dead simple. Anyway, thanks for the explanation of Garmin vs USB modes. I really had no idea what those were all about.

I would push hard for an explicit setting to control behavior when removing external power. Personally, I would be afraid that the current behavior is a bug - and might disappear unexpectedly some time in the future.