You could put 2x CR123A camera batteries in series and you would get 2x3v=6v at 1500mAThen you could simply use a tiny resistor to reduce that 6v to 5v.
Indeed to go from 6 to 5V I need a 5V regulator. The problem is that for 5W I need also a dissipator , don't know if it fit in.12V led => car battery could be the solution but a little too big I'll take a look at thoose CR123A ih they can draw 5A
I reread your post and realize that you expect to be using these strips.What an inefficient way to run LEDs. One can see the individual resistors.