Battery Compartment humming

Couple of things I think you are confused about...
First, your water heater is not heating on 12v. It is either heating on shore power or on gas.

Second, My bet is that the hum you are hearing is not batteries but the fan that is cooling your converter. That's normal.

Not hot water is probably because your winterizing by-pass valves are in the wrong position OR the outside shower is not shut off. The outside shower valves (hot and cold knobs) must be off, not just the button on the spray head.

Not on shore power, batteries and gas.
Water is hot, just not real hot as I would expect to mix some cold to use.
Outside shower is off.

You can't pinpoint the source of the noise?

2oldman wrote:
You can't pinpoint the source of the noise?

Battery compartment, it's very open, can get half my body in. Maybe strongest at the positive trailer connection. I have a video if someone can tell me how to post it?

As long as it's not humming "Nearer My God to Thee", it doesn't sound serious...

It sounds like a harmonic thing -- something in the compartment is picking up a vibration from some other area. If you press against any side, back, or door of the compartment, does the humming stop? Is there anything loose inside that could be vibrating? Battery tray? Cables? Electronic box attached to a wall? I'll bet it's something like this that's causing it.

Many years ago I bought a mechanic's stethoscope like below, and have used it numerous times to find oddball sounds.

I have a video if someone can tell me how to post it?

Make yourself a YouTube account and upload it there, then share the URL.

Steve

That seemed easy enough.
https://youtu.be/XJIGED-dr0Y

I get no sound when playing the video on computer, but sound is there on my phone?

Hmm. Since it's only the WH, on gas, I'd check the regulator. Sounds can travel ya know.