I'm working on a solar powered project which requires two voltage levels - 3.2v-4v @ 2A for one element an 6v-12v @ 500mA for another.
My initial plan was to use a 12v lead acid battery with a solar panel and a charge controller. I would then regulate the voltages. However, the size and weight of lead acid batteries is a bit of a concern for this particular project and so I looked into using a lithium battery. The problem I had with this was that I could only find solar charge controllers for 3.7v lithium batteries, nothing for higher voltage lithium batteries (no decent ones at least).
I came up with the idea of using two 3.7v lithium charge controllers. I could then use one of them to power the 3.2-4v element while also using them in series to power the 6-12v element. Of course the overall Ah rating would be the lowest of the two and they would discharge at different rates. I'm wondering if this is still a feasible solution though. I've added a block diagram of my idea below. I'm open to other suggestions too.