I have experienced charging problems running a 12v ignition from one battery on a 24v system. It takes a few months but one battery ends up drained and the other overcharged.

I am adding a dc/dc converter that I think is necessary to cure this imbalance.

I would like to hear if others have experienced this problem. My mechanic says it is not a problem and is commonly done, ie drawing 12volts from one battery, but everything I have read says it is a no, no.