Originally Posted by Lakesidemn
I have a 2015 RoadTrek with a new inverter and 4 new AGM batteries, installed Spring 2018. Everything was working great, but then I mistakenly left the Inverter turned on. It was on for a couple of weeks and drained everything to the point where neither shore power, or the on-board Mercedes engine generator, will charge the batteries. Any suggestions would be appreciated. The display on the inverter won't even light up! Thanks.
Hello and welcome to the forum!
There are 3 subjects involved in your question: inverters, battery chargers and battery condition.
Clearly, the idling load on your inverter discharged your batteries but before you go and burn down the RT factory, understand that all inverters, even the best of them, have significant idling loads in the whereabouts of a couple of amps. However, the Roadtrek inverter consumes even more than that at idle - somewhere around 5 amps, so it can discharge batteries in fairly short order. What's less appreciated is that even when inverters are shut off, as long as their input leads are still physically connected, they can still consume trace (milliamps) amounts of power. Both Xantrex Prosines and even Magnum units are examples of this. So, the best move when leaving the coach unattended is to hit the battery disconnect switch prior to leaving.
"Smart" charging technology can drive you nuts. Because of the low terminal voltage of the fully discharged battery, in their infinite wisdom, the alternator or the shoreside converter/charger concludes that there isn't any battery there at all and refuses to cooperate. This is even the case with typical current production external chargers which when hooked up to a dead battery will report that the battery is unusable and will refuse to come to the rescue. After dealing with that frustration for years, I threw mine in the trash and bought a "smart" battery charger that would report the same symptom, but had an override button that would at least attempt charging regardless of the battery condition.
Considering that your discharge period is in the whereabouts of 5 - 6 months, the prognosis is a little dubious. When lead sulfate produced during discharge becomes crystallized on the plates, it's reluctant to return to a pure lead state and even if the battery will recharge, it's capacity is typically diminished well below its design capacity. Some batteries like the Concord Lifelines will bounce back better than others.
Since the batteries were so recently purchased, aren't they still under full replacement warranty? If so, consider skipping any recharging effort and see if they qualify for replacement under that warranty.