I am working on my mountain cabin and am wiring it with some new electricity. In the long run, I want to switch to only LiPo based batteries but for now I still want to keep my old Pb batteries as a backup. I have two new and very strong 400 W panels which I use to charge my LiPo pack and I use a separate charger for my old Pb pack since connecting panels of different power can significantly decrease the power output of the stronger panels.
What I want to achieve somehow is that I can use the peak power of the five batteries all together when I need it for example to heat water, solder, run my 3D printer etc. I know that connecting them is not a good idea because of the different discharge characteristics and voltage levels. I could just put a simple switch and use either or but of course would loose my maximum power output.
Which circuit could I design to put at the [?] that somehow combines the output of the two sides? Please note that each battery back can deliver up to more or less 100 A so anything placed where the [?] is, needs to sustain high currents.
So of course, any form of parallel or series connection is off the table because the batteries have different voltage and current specs. Would it be sufficient to run the positive wire through diodes for each pack to avoid back-flow of current to the other battery pack?
Edit: my current idea is to connect a buck converter to the LiPo battery to pull down the voltage to around 12 V before I merge it with the Pb battery. The Pb battery behaves very soft, i.e. it will have a decreasing voltage on high load. Through this, in the moment a high load is operating, both batteries can start delivering power.