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This pretty much points to some battery issues. Dirty cables or batteries that are failing will cause a host of symptoms such as you describe. I would start by having them load tested and checked for shorted cells and clean all cables including the ground lead to the chassis. Be sure you take photos of the cables and hookups so you get them back the same way again. Easy to get this wrong if you don't Most places that sell batteries can load test them for you. Over 3 years old and they may be toast. Let me know how that goes and once we rule that out we can dig deeper if needed. All follow ups are included in our fee.