Series/parallel batteries

Hey guys, i was hoping somebody could help me with this. Im trying to wire 2 26650 batteries in series and in parallel at the same time that is switchable between the two. Can someone atleast point me in the right direction, i know its able to be done. Please and thank you in advance.

What sort of “switch” do you have in mind?

Just a 2 way slider…maybe one with an off selection, i want to be able to switch between parallel and series when the need arises

A DPDT wired this way. You can probably find one w/a center off position as well.

Batteries in parallel. Not. One will discharge into the other to reach equality. But due to leakage, they’ll both discharge faster.

With diode isolation you can.