Alternative Solar Chip with Diode

Since my previous attempt to revive my old solar chip didn't succeed, I got a new Idea. And that was to make a solar chip myself. First we have to have the ability to load a higher voltage battery with a lower voltage battery, and that we make possible with a diode. This diode, like you see in the picture, makes sure that the current flows in one direction.

Now, we need to test this diode theory, so I connected a lower voltage battery 4V with a higher voltage battery 7V. If the test works, the higher voltage battery will be charged by the lower voltage battery. This test worked, but I don't trust it, so I will be doing another test.