I have a solar charge controller which can charge 12volts batteries. I have two 12 volt batteries which are connected in parallel. I need to have 24volts output without using dc-dc step up converters. Can I connect two 12 volt batteries in both parallel and series? like first having a parallel then having a series connection with some Diodes to control the current/voltage flow. Is it possible? are there some best practices?
On the face of it, not really unless you use switches to take the batteries offline while you charge them.
Now if you can use 2 chargers, and the chargers have a floating (ungrounded) output, you could connect each one across each battery. If the batteries are to be kept online ensure that the charger has current limiting and reverse-current blocking.