Mako,
Ya, taking breaks from sealing projects is a good thing. When I restored my roof, I did it over many days of work with breaks as I deemed necessary. FWIW, I had many areas of different sealers to remove including a gallon of asphaltic roofing tar. After using Eternabond tapes over everything, I don't have any leaks.
I'd suggest to see what your present converter does and then reason if that will work with your intended battery system. Some renovators install new batteries and the old converter isn't up to maintaining them well. This is observed by using a meter and measuring the output of the converter along with the state of charge of the batteries. If you are thinking of installing 2 6V batteries and use only the converter to charge them, replacement of the converter is best. These older converters won't supply the higher voltages those batteries need, a new PD converter will supply that voltage.
Having said the above, here's my situation----I have five batteries in two banks. They are charged by a solar panel. I kept the original PD 808 converter with added battery charge circuit (a 1971 innovation) to offer battery charging in an emergency situation. I know the old ('71) converter only outputs 30 amps at 13.6V but it will get me by until the sun shines or I arrive home where larger chargers are available. I also travel with a stand-alone battery charger since I'm dependent on the 12V system for refrigeration and entertainment devices when not on a shore cord. There are different solutions for different uses.