I have a diesel heater straight to battery which is usually fine for the hour blast I need. However going away with the gf in the cold so going to be on longer. Wondering if I can get away with buying another car battery or even a leisure battery and linking jump leads to the 2 to give myself extra ah. So then when disconnect I hopefully still have power to start van after a few days. I also have a booster to jump start if take it to far.