why not consider USB charge?
Where are you going to fit a USB jack in a Mini3?
Simply put a mini B socket on this new board upon the original DC jack, desolder the original DC jack, it should fit the hole originally for the wall wart, for postioning for USB socket, maybe need something like s SMD to DIP opamp adpater, to make the mini B socket fit the postion of the panel hold
If for charing only, a simple 5V step up should make the USB cahrge idea work, of course the curent not as high as a wall wart, which will takes longer charging time, but in real time there should no need for rapid charge.
Long battery life is convinence for outdoor, therefore my point of view is all target to outdoor application, USB charge also convience for outdoor, in case we need to charge outdoor, or at least not at home, nowdays around the world maybe find a USB power supply will be more easy then find an AC mians for a wall wart; And in case we need to wait for charging outside, one hour or three hours waiting may not be a big difference when outdoor, since I don't think user will willing to wait for one full hour even could rapid charge by a wall wart, mostly in real life will only charge up for short terms, enough for arrive the destination will be fine.