6-months is about normal if the battery depletes to 0.0 volts when no master shutoff switch can chop every last milliamp of drain. Combine that with sucking the battery down overnight until it wrinkles with a high draw furnace fan and wait there's more! Under feeding the battery the battery with a snotrag converter all combined adds up to exactly what you are reading in the OPs plea. Not enough battery - a Dr Mengele grade converter and no way to stop bleeding down the battery adds up exactly to this grade of woe. No single fix will cure this.