Here is the situation: I have a wheelchair powered by two 12v bridged batteries (24v). I like to have 12v output to power a laptop computer. I estimated that I need less than 4A. I do have access to batteries and I think that I do not need to use very expensive 24v-12v converter. It is a way to build circuit using for example diodes or something like this to achieve 12v output. Thanks for any input.