Remove just the converter part (4 screws if it is a Magnatek) and wire an inverter/charger into your existing circuits. I just finished the job, and I'm happy with the results - batteries last longer and charge quicker. (I started a thread
here), Don't make the same bone-headed mistakes I did :).
If you don't want to go with the inverter/charger plan of attack, I recommend replacing the unit with a Progressive Dynamics unit, which is a smarter charger, but still a converter. Many threads on this topic, including tutorials, etc.
The first step is determine your model number and proceed from there. There are dozens of youtube videos on the subject.