I suggest you call Magnum Energy's Technical Support and have them lead you through a diagnosis of your Inverter/Charger. They are excellent to work with. I had a similar problem and working with them over the phone they discovered a bad temperature sensor which was causing the batteries to overheat. Their phone number is 425 353-8833. BYW an inverter does not charge batteries it only converts DC voltage to AC voltage. It is the charger side that charges the batteries. Leave the inverter turned off when not in use. If they discover a problem you can send your unit to them for repair at a fraction of the cost of a new unit. They are in Everett Washington, not to far from you.