I'm thinking of developing a pocket 'power bank' that could provide both 6V and 12V - a charger to charge either a phone (with 6V) or a notebook computer (with 12V).
The electrical diagram is simple enough; switch attachment of the terminals like below.
The schematics is not everything though. I'd like the charger to have two sockets, one providing 6V, the other - 12V, and to "sense" what to serve by having a plug in either of the sockets (let's say using both at a time is forbidden; I can place them in such a way that both plugs won't fit at a time, say, a slider that opens either of them but never both).
Best if the "sensing" was done in the simplest, mechanical way (e.g. there are sockets that provide an extra "sensing" contact that shorts to mass if the plug is in), but if that would prove too difficult or mechanically complex, a more complex electronic solution would work too, providing it won't drain the batteries when nothing is plugged in. (and of course the circuitry must accept external charging current - accepting only one of the two, either 6 or 12V is fine).
And of course while just cutting one of batteries off for 6V would be the easiest solution, it would halve the capacity for 6V application and cause parasitic charging issue when switching to 12V after the 6V power has been depleted, so it's not really an acceptable solution.
So, how to build such a circuitry - that provides power from two batteries, in series or in parallel depending on which socket was used?