Contribution #1 by Entunassa:

I´m not very experienced into MPP trackers and not into programming also. We have to check different concepts or existing schematics for what we can use.

https://www.researchgate.net/profile/Abdelhalim_Zekry/publication/290436504_Enhancing_the_design_of_battery_charging_controllers_for_photovoltaic_systems/links/5baa2d1645851574f7e441f8/Enhancing-the-design-of-battery-charging-controllers-for-photovoltaic-systems.pdf

(this is one of the finds from "the internet"...)

I suggest a modern software approach that yet fits in a tiny PIC or ATMEL; my hope is to find a tiny program which maybe can be translated to the 4004 system without pushing its boundaries.

https://ww1.microchip.com/downloads/en/appnotes/00001521a.pdf

It could help not to re-invent the wheel, but rather have the focus on the conversion to the 4004.

-/-