Electric - Event Date: 18 Nov 2019 - 28 Nov 2019

WFCO is the manufacturer of the battery charger in the trailer, which is located in the bottom of the electrical panel. Even if your battery is completely dead it should be able to provide enough current to bring the slide in, assuming it is operating.

So if the slide starts in for a few seconds and then stops you have a dead battery and its not getting charged. The WFCO chargers are not the most reliable things in the world. I would start by checking all the fuses and breakers and then connecting to a known good 120Vac source (to avoid the possible low voltage issue StephenH raises) and see if that brings your battery voltage up. Although its a good idea to have one, you can tell even without a DVM because the lights, fans, etc will start to get brighter when you turn on the charger. You can also use a separate portable battery charger connected directly to the battery terminals if you have one handy. 

Your battery has been completely discharged, which is not good for them, they can only tolerate that a limited number of times. After you get your charging system fixed and the battery fully recharged you might find that it won't hold a charge, so you might need a new battery too at some point. 

A DVM can show a low ac voltage condition under load just like an analog meter, all you have to do is connect it while the loads are turned on. That can be done using one of the trailer electrical outlets. 

Mr. Coffee is pure resistance heat. It is not as sensitive to low voltage as things that have electronics and motors. I suspect that the voltage at the post was low, essentially giving you brownout conditions. A digital voltmeter is definitely a good investment as is a good circuit analyzer that plugs in to the post (or hard wires, your preference). We have a Camco one that is basic, but did spot a faulty post at one campground where we changed sites. I am glad I had not done all the setup first.

There is a plug-in voltage conditioner that can boost low voltage, but it normally costs an arm and a leg and a firstborn child. However, Amazon has the Hughes Autoformer right now at $339.70, which is a bargain for what it does. I just ordered one since I have been waiting for them to come down in price. That is over $80 less than I have seen it selling for before now.

Digital Voltmeter?