I just purchased a used 2003 Coleman popup and the battery needs replacing. I do not intend to use shore power, the battery will only be used to run interior lights (LED) and occasionally the propane heater fan as well as charging my cell phone via USB. My truck is only equipped with a four-pin connector, so will not be charging the battery while running. I hope to purchase a solar panel to charge the battery while camping or parked at home. Any suggestions on a battery and/or solar panel system? I am on a budget ...