Seems like the expectation is for the engine alternator to fully charge the starting battery's, which it won't, as it was designed to top off a fully charged starting battery's. Our house batteries are charged by the generator and shore power. We took our 10 months old batteries back to Interstate where we learned that. They re-charged the starting battery's at 10 amps and it still took 36 hours on the industrial charger they have for a full charge. Our alternator finally failed and needed replacement, it can strand you if and when it expires. When we replaced the alternator we learned of its capabilities. Everything 12volt improved with that replacement , lights got brighter, ABS light never came on again. Then charging wasn't an issue because we were driving daily. Our alternator always appeared in good shape and had been tested by many technicians, just never under a load and that's where it was weak, how we don't know. Bottom line shore power charges house batteries and engine alternator tops off charged starting batteries. We put a charger monthly on the starting battery's to keep them up to fully charged when we're not driving. Hope that helps. Although many say shore power should charge everything it 100% does not on ours and all systems are functioning properly.